I'm fairly sure, as has been mentioned, this means that any person from the team who should serve, can start serving the first game of the set.
If team 1 is A and B, they have to serve their games in set 1: A B A B A.
But set 2 A can serve first again (e.g. A B A B A - A B A...), even though they served the previous game that their team served.