The important thing to remember when building your team is that Chemistry certainly matters. On your lineup page, you will notice that little green bar in the top right corner; this represents your chemistry on a scale of 1 to 100. Reaching 100 Chemistry is well worth it as you will notice the drastic change in your teams ability to win games, in a positive way. Chemistry is determined by nationality, formation, position, and your manager. By playing players next two each other who are alike in nationality, you will boost your chemistry. If players are in their preferred position and if they play in their preferred formation, which you can change, your chemistry will rise. Likewise, your manager has an effect on your chemistry in that if he is playing in his preferred position and/or has the same nationality of at least some players on your team, this will boost your chemistry.

You should try to organize your team in such a way that your chemistry is high, but your team still features good players. This is why it is good to pick a nationality who has an abundance of good players instead of some country like Togo, that really only has one very good player; Adebayor. You might also want to consider matching nationalities by defence, midfield, and offense. By this I mean that it is possible to achieve high chemistry by having a Portuguese defence, a Spanish midfield, and a Brazilian attack. Formation cards will be expensive, especially for popular formations, but well worth it because of the chemistry boost they provide.

Also note that it is impossible to surpass 100 Chemistry, and there are no "hidden bonuses" of adding formation cards to an already 100 Chemistry team, for example.