Question: How do I play with friends?
Answer: You will be able to compare your performance with your Facebook friends and see their scores in Stats > Brain > Compare your performance > Friends. The comparison includes the PBS, Peak Category Scores and all the game scores (with a 'winning', 'losing' and 'draw' section).
Also, after playing any games, on the score screen, you will be able to see which friends' scores you beat (if you manage to beat them).