Tiebreakers are used to distinguish between teams with the same record. Each league can customize its tiebreakers. If teams are still tied after applying one tiebreak, the next tiebreaker is used. Teams are ranked by their win-loss (and tie) record.

Yes. The commissioner can configure the league to break ties in head-to-head matchups. Some leagues opt to allow ties.

You can edit tiebreakers by going to League » Settings » Edit Tiebreak Rules. You can drag and drop the order in which tiebreaker you want to use first.