A few things to consider:
Are you intending to be a long term investor? That is, you're buying part of a business (shares) and intending to profit from the long term success of that business through both dividends and a rise in the share price?
First thing to understand there is that in buying shares you are buying part of a real business. You'll want to be able to understand the businesses you're buying part of and evaluate its future prospects. You'll also benefit from at least a basic understanding of technical analysis to assist with timing your share purchases.
Or are you intending to frequently buy and sell shares with the intent being to profit from short term movement in the price of those shares and with little or no interest in the underlying business?
In this case you'll be focusing on technical analysis and looking at charts. You don't actually need to know what company XYZ even does in order to do this although some basic research may help to avoid some risks.
Something to understand with any long term investment stragegy is the importance of dividends. Dividends - that's cash (cheque or electronic payment - they won't send you actual cash in the mail) paid out by the company to shareholders from the profit it makes running the business. Not all shares pay dividends but those that do generally pay an interim and final dividend each year - so you receive a payment roughly every 6 months.
Consider as an example someone who bought shares in CBA (Commonwealth Bank) in late 2008 after the financial crisis caused the value of those (and most other) shares to fall. The actual lowest price for CBA was about $25 per share but let's assume they bought at $30.
Since that time CBA has paid out $25.55 in dividends for each share, so that's an 85% return (based on a purchase at $30) over that time and even better is that the dividends in this case are 100% franked (in simple terms that means they've already paid company tax on the dividend payments, so you won't have to pay that tax again on this income). And that $25.55 is profit in addition to the fact that the shares themselves are now worth over $75 each.
CBA is just a random well known company that I picked for the example. I'm not suggesting that you should or shouldn't invest in CBA, it's just to illustrate the point that dividends can be important if you're holding the shares for a long period.
Both approaches, long term investing and active trading, can be successful if applied correctly.
Some other thoughts:
Size of trades / investments. Whatever you do, keep it small when starting out. Only invest a few % of your funds into any one stock and remember that you WILL make poor choices at times and end up buying things which result in losses. Keep it small and that'll keep your stress levels under control as well as ensuring you don't manage to lose the lot through one poor choice.
How to actually buy shares? You'll need an account with a broker to do this and there's two basic options here with numerous brokers offering such services.
An online broker will generally facilitate the transaction and that's it. Their site may include some basic charts and other research tools but the fundamental purpose of their business is that they enable you to buy and sell shares, that's all. The broker won't provide any advice on what to buy, all they do is facilitate the transaction and that's it. Mainstream examples of such brokers are CommSec and ANZ Share Investing (formerly known as Etrade) but there are many others too.
A full service broker means a human sitting in an office and you'll have access to them either by going to their office or at least over the phone. They provide advice on what to buy as well as facilitating the actual transaction but the advice is primarily what they're focusing on (some will simply use a third party online broker to make the actual transaction). You'll pay a lot more for this service than with an online broker since you're paying for their advice as well as making the actual transaction. Depending on the approach you want to take, such advice may or may not be worth paying for.
Risk is a complex area and there are many risks affecting any investment. Broadly speaking, if there was zero risk then there would also be little if any profit (since if it was really zero risk then everyone would be doing it). So you can't avoid all risk and even keeping cash in the bank isn't totally without risk (inflation will erode the real value of cash over time, albeit rather slowly at the moment).
Market risk - things like the Global Financial Crisis resulted in most shares dropping considerably in value at that time. So did the 1987 share market crash and various other events over the years. They were great buying opportunities for those with cash at the time and who took advantage of the low prices to invest but it wasn't so good for those already invested and who didn't sell their shares before the slump.
Industry risk - if the entire industry that a company operates in turns bad then it's going to be hard for any company operating in that industry to do well. Some will do better than others and may come out of the downturn stronger than before but in the short term they'll still be affected. Weaker businesses may well go broke if the underlying industry struggles. An example would be iron ore miners - the stronger ones will survive the fall in price but the weaker ones may either go bust or at best be taken over by the stronger companies.
Business-specific risks - something like an airline always has the inherent risk that a plane could fall out of the sky. That doesn't mean you shouldn't invest in them, someone who bought shares in Qantas 18 months ago would have made a 200% profit over that time and that's definitely a good result, but the underlying business activity is itself not without risk should a major accident actually occur (Qantas has a great track record, I'm not saying they're bad in some way, but planes in the air = definitely more risk of a major incident than with something like a supermarket chain).
Company financial risks - it wouldn't be the first time that a company had a profitable underlying business but managed to go broke because they messed up currency hedging or some other financial deal. The factory or whatever was profitable but the company itself went bust.
How many underlying actitivies the company has is also a factor in risk. A company that relies heavily on one major contract to do something is in trouble if they lose that contract and can't secure a new customer quickly. There's far less risk if the company has 100 smaller contracts with different customers since they're unlikely to lose the whole lot.
Political risks - if the company's business is subject to political debate with a clear impact should a different party be elected then investing in that company's shares is at least partly a bet on the outcome of an election. This thread isn't the place to discuss politics (there are threads in the ASF General Chat for non-share market topics like politics) but it's a real risk for some specific companies involved in politically contentious industries.
Then there's the less tangible things. Personally I don't like investing in anything run by "larger than life" high profile managers etc. I'd prefer they spent their time running the business rather than engaging in "stunts" to promote the product, pursuing their political ambitions or otherwise getting themselves in the news. There's nothing wrong with the CEO making themselves available to the media for interviews if there's been a major company announcement or something like that, but it worries me if they're constantly trying to gain attention for the sake of it. At best, their mind clearly isn't focused on running the business as such.
And of course there's your own tolerance for risk. What do you hope to achieve? Are you attracted to the idea of owning part of a business that is predictable and returns a modest profit to shareholders each year? Or are you hoping that your investment in some small exploration company really will find oil and make you a millionaire by the end of next week (with a very high risk that they'll find nothing when they drill and then go broke)?
Some people will also have an ethical consideration in investing. If your political or moral views are opposed to (to pick random somewhat contentious examples) coal mining or detention centers then you may decide that you don't want to invest in companies involved in such activities either directly or as contractors to governments. Others will conclude that the activity will carry on with or without them owning part of it and just focus on the financial side alone in deciding whether or not to invest in it. That's a personal choice and I won't lecture anyone there other than noting that it's something a new investor may wish to consider.
I don't give "tips" but I'll give you this one.
Always remember that the market will still be there tomorrow. Learn, start slowly and don't be in a hurry to have 100% or even 50% of your money invested. Get started yes, but remember that you WILL make mistakes so you want them to be with small $ amounts not the whole lot. Start slowly and build up from there - the share market isn't going to disappear anytime soon so there's no reason to rush and take unnecessary risks.