Matches are created by the coach or an administrator: in “Calendar” tap “+”, type the two teams in “Home” and “Away”, choose the “Date and Time” and tap “Create match”. With “Manage Call-ups” you can say straight away who is called up: in that case the team gets the “New match” notification.
The call-ups are changed from the “Call-ups” row in the match details, until the match is finished. They apply to everyone: in the fantasy lineup you can only field called-up players.