There are lots of highly paid experienced traders (the kind of Mumsnetters and their DHs in their 'big jobs') who do this for a living. Only a minority of them make a better return than index tracker funds.
If you want to make an income, rather learning to be a trader, you'll almost certainly be more likely to be successful by just buying diversified tracker funds in a S&S ISA.
But there are apps to help you trade now. You're basically wanting to buy and sell for a profit, so need to buy low and sell high. I think the 'quickest' way to do it is to repeatedly trade, so buy share X, then sell when the price has risen and you can make a profit, then use that larger amount of money to buy some different shares, which you then sell, then so on.
But you have to account for the cost of trading, so can't start too small or else this will wipe out your profit. The time period is hugely variable. There's such a thing as day traders, who buy and sell within the day, to exploit variations in the market, but they're working with huge amounts of money and it's very risky. Get it wrong and you could lose thousands.
Others will keep the shares for longer, to wait until they can make a profit, but obviously that lengthens the time it takes for your income to grow. But that might introduce dividends into the mix. I think some traders time their share purchases to qualify for dividends, to make money that way.
I think that trading would also be subject to capital gains tax if you exceed the allowance, and the shares are not in an ISA, so that's also something to make sure you understand.