It depends on what you want to know about?
Is it the basic concepts of investing in stocks and shares yourself or are you looking to invest in funds (a fund is a set of stocks/shares managed by an experienced fund manager(s))?
In general, a basic rule of thumb is that the higher the risk, the higher the potential yield (and the higher the potential loss).
At the safer end of the scale, you have things like government bonds. They're typically low yield, but very safe (until, well, things go nuts and governments have to step in to guarantee them).
At the riskier end of the scale, you have hedge funds. You've probably heard of them recently, but it's a bit like a form of gambling. You gamble on how the price might go in the future (not necessarily that it will go up). So you don't buy a share in Apple and hope that they bring out a very popular new phone from which they make billions. Like what happened with some traders making millions from betting AGAINST the value of the pound recently. Hedge funds are the ones I know least about.
Then there are things like currencies and commodities. Currency trading is commonly referred to as Fx trading. If you're in the US and you have dollars, now would be a good time for you to convert them to GBP and then if the value of the GBP rises against the dollar then you could convert them back into dollars!
I'm not in the industry but have a very basic understanding of most of the concepts. My little brain gets fried when people explain things without a diagram lol.
If you're wondering about what to invest in, if it's significant amounts, I'd put it into a fund (they vary in terms of risk/%yield). If you want to toy with buying a few things yourself, then you figure out what you think might rise in value and buy that (and sell it when it's hit the top).