Free Play Mode is very similar to how it is on the Console version. You pick any character that you've unlocked and try to find the collectibles in the stage.
In this version though, you can only select one character and you won't get anymore aside from what you already got in the Story Mode run. There are 5 Death Star Plans per stage, and collecting all five in a stage gives you a new code to use.
There are very few differences in characters this time around, here is the short list:
Astromech: R2 and R4 have the ability to hover for as long as their force meter allows, as well as being able to use panels. Unlike the console versions, they will be attacked by enemies.
Blaster: These characters don't have as high a jump. But have the perk of being able to attack from a distance with a blaster. Eg. Amidala, Tusken Raider, Jango Fett, Clone Trooper, Chewbacca.
High-Jump: Jar Jar has the ability to jump the highest out of any character in the game. Darth Maul also has this ability, making him the best character in the game.
Jedi/Sith: Bringers of Peace for the good guys, and the opposite for the bad guys. They can jump slightly higher than others and can use the force on various objects. Also uses a Lightsaber, the best weapon in this version. Eg. Qui-Gon, Obi-Wan, Anakin, Yoda, Dooku, Vader, Maul.