It is not currently possible to play against your friends. For races, the opponents you race against are selected at random. 

You can however create or join a Club with your friends, as well as connect your facebook profile to see which of your friends are playing F1 Clash and compare your progress. 

When you sign into Facebook in game, the game will ask you to give us permission to access your friend list. Please confirm it and you will be able to see your friends who play F1 Clash in game. Your friends will also need to connect Facebook and confirm the permissions for them to display. However, it's not possible to remove them from the game if you delete your friend on Facebook.