You can enter your own World Cup Fantasy team at http://www.fantasyfifaworldcup.com/ - You will need to register first, then go to 'Manage My Team' (top-left corner, under your name) and choose your starting 11 (1 keeper, 4 defenders, 3 midfielder and 3 forwards). You can only choose 1 player per national team, so you can't have Xavi and Iniesta at the same time - Sorry.
Once you have chosen your 11 stars, you need to go to 'Join Personal League' (again, top-left, under your name) and enter the code for the 'FC Barcelona' league which is 95232. To check that you have done this right, go to League Table (Top-right), then 'View My League'. You should see the 'FC Barcelona' league there. Any problems, let me know: Comment
You now need to invite all your friends to join, the more the better! Spread the word by pressing this Share button. Do you have what it takes to be the World Cup winner?