I probably made somewhere around 500 doing this a while ago, so it is possible.
When talking about matched betting, in essence I think of this as taking advantage of the bookies free offers.
The way it works is you sign up with a bookies that's offering a "bet £x and we'll give you a free £x bet"
You place the initial bet with the bookies, and then lay the bet (that is, bet on the opposite outcome) on the exchange, usually Betfair.
Unless you're very lucky, this leads to a small loss overall, however you've then got a free bet to play with at the bookies.
You then repeat the process with the free bet, so say back a horse at the bookies, and lay it on the exchange. Whatever the result you're either up at the bookies or up at the exchange. Take off your initial loss, and this is profit.
Then repeat with the next bookie offering matched bets, and so on...
It's a bit fiddly, but there are a few websites that can walk you through it.
However... be aware that it can make your bank nervous if they see a number of gambling transactions going through your account. They won't stop you doing it if you've got the funds, but for things like large personal loan or mortgages applications which can go to underwriters for assessment, they see it as an additional risk. They won't understand it as a profit making enterprise!
For that reason, I'd be tempted to set up a completely separate account with a totally different bank to run this through.
You also need a bit of seed funding for this, maybe a couple of hundred quid. That's mostly to fund your exchange account. It's advantageous to lay at quite high odds sometimes to maximise your profit, so you need a reasonable amount on tap at the exchange to do this.
So, it's do able, but it's quite hard work if you're serious about it.
Most importantly though, if you want to make money rather than lose money, I'd avoid getting pulled into the world of betting for fun, unless it's with money you can afford to lose. There aren't many poor bookmakers.