Once you have an account and login for the first time, you are asked to change password, specify your team's colors and to add players to your team.
If you are looking to add players at a later stage, you can always access your squad and add players by going to Settings (the gear icon to the right of Home).
And then taping Squad.
To add a player, simply fill in their First name, Last name, Shirt number and Position using the form
NOTE: If you already have players in your squad, you will find the Create player form at the bottom of the page.
When you have filled all the fields, simply tap the green CREATE PLAYER button.
You should now see the new player being added to the list.