Mining it is solving mathematical problems. These problems are used to verify the transactions. As a reward, for each transaction you verify, you get a tiny cut.
Trading Bitcoin is probably pretty identical to Forex trading. You stick a large lump sum in, say 10k, and when the valuations fluctuate you trade currency to gain a profit. Trading currency is probably just gambling really.
Because you need a large lump to do it properly, again I wouldn't bother. Your returns on trading small sums are not worth your time.
Best bet? Stick £200 a month (or whatever you can save) into Bitcoin. Once you have a few bob, buy a proper hardware wallet. Each month buy the currency and stick it on the wallet and keep the wallet safe.
In 10 years, you stand a good chance of having a nice lump of cash on your wallet worth much, much more than what you put in.