If you're familiar with the movies of Jason Statham (notably the 'Transporter' series), you know what a Cockney accent sounds like. So why not watch this video to learn about the various features of the Cockney accent, and even take a little test at the end!
OK, I'm guessing you realized it's not really Jason Statham, but I reckon he does a pretty good impression. The video was created by Aly Williams and Tom Turner who run the Papa Teach Me website. You can find more of their videos on their YouTube Channel, where they have a playlist devoted to the British accent among other things.