Hover over Competitions and select Team Setup.
Click on the name of your team.
Click on the Fixtures tab. This will list all the games your team is playing.
Click the Confirm Members button next to the game to which you need to add players.
This will give you a list of members on the left. You can use any of the filters to narrow down the list.
Click the green arrow to select a member to play. The names will move to the list on the right. Click Save.
NOTE: when adding members, you can include the coach and team manager.