After Season 1, teams finishing in the top 7 places get promoted to level 2, with the top 4 also qualifying for next years Champions League. As you move up the quality is higher so a 7 star player on last day of this season will be shown as 6* on the first day of next (but the quality values are the same); your players will be a year older and 1 year less on their contracts. Older players can retire if old enough, out of contract players can be resigned or allowed to leave etc.

Other than that it just all starts over again - new season, new rivals, new challenge.