Heres some stuff you can unlock:
Super stories: to unlock an episode's super story, you must beat all the levels in the episode and collect the required number of gold bricks.
Bounty hunter zone: to access the bounty hunter zone, you must unlock all of the game's bounty hunters (for those who don't know, the bounty hunters are boba fett, bossk, 4-LOM, IG-88, dengar, and greedo).
Lego city: to enter lego city, you must collect 60 gold bricks, and then go outside the cantina and build a giant ? Mark with them.
Stud fountain: to get the stud fountain, you must collect all 99 of the gold bricks in the game. Afterwards, go outside the cantina and construct an imperial star destroyer to unlock the stud fountain.
Extra characters: to play as normally unplayable characters, simply buy the extra toggle option from the extras menu. Turn extra toggle on, and when you go to a level, you will have a few extra characters. Good luck!