To add a user to your friends, go to Menu > Friends and search for them by their Facebook name (in case they are associated with Facebook) or by their username. Once you find it, select "Follow". In this way, you will be able to play together and, if said user is associated with Facebook, they will appear in the weekly ranking.
Remember that you can also invite friends via link through different social applications. To do this, follow the following steps:
1 Press the "Send link" button that you will see in the lower left corner of your screen, along with your current games.
2 Once you do, different social applications will be displayed through which you can invite your friend to the game.
3 Once your friend receives and accepts the invitation, they will appear as a friend available to play every time you want to start a new game.
If you want to invite another friend, you will have to follow these steps again.