The description on the website and your Xbox may be different, but for this achievement you need to complete a 20 minute joyride online with at least 3 other people, on the battersea compound. From the main menu, select Multiplayer and then Xbox Live. Now select "Jam Session" and custom match. Change the discipline filter to "Joyride", and search. (You can also create a match instead). Now just find a game with at least 4 total people and play it from start to finish. It can be hard to find people who won't kick you out after you wait for a long time, so you can find partners to boost with here.