LEGO Star Wars: The Video Game/Character types

There are several different kinds of characters: Jedi/Sith, blaster characters, battle droids, protocol/automech droids, and others. Characters of the same type are mostly the same.

Jedi/Sith
The Jedi and Sith use lightsabers and the Force.

Lightsabers
Lightsabers can block attacks and reflect blaster shots. Attacking also blocks lightsaber attacks and blaster shots. On the ground, tapping B repeatedly does a lightsaber combo. If you jump in the middle of it, the character will turn around with his/her back to the enemy and do a backflip over him/her, which can allow you to do a midair attack. In midair, there are two types of lightsaber attacks: forward and down. The character will stop in midair and attack/fall straight down if you attack after a midair jump, but if you don't midair jump, he/she will go forward and attack. The exception is that after a jump in the middle of a combo, a midair attack goes straight down.

The Force
The Force is used to interact with certain objects in the game. You can use the Force on objects glowing the color of your lightsaber. Some Lego structures can be taken apart and put back together or moved with the Force. However, you can't control it, the game automatically moves the pieces. It can also be used to push some enemies away. Also, unlike most others, the Jedi/Sith can midair jump, possibly using the Force.

The Dark Side
Sith can use the Dark Side of the Force as well as the normal Force. The Dark Force can be used on black Lego pieces.

Blaster characters
Characters with blasters can shoot and grapple.

Blasters
Blasters shoot lasers at enemies. The lasers can be blocked by lightsabers and Droideka shields, however. The blasters automatically aim vertically, so you don't have to go on top of a platform in order to shoot up to an enemy. Also, the Wookiee's crossbow counts as a blaster.

Grappling
Blaster characters can grapple up to platforms and across gaps at certain places marked by red circles, using X. This is used in several chapters to reach high and far places.

Battle droids
Battle droids are droids made for combat. They are equipped with blasters, however cannot grapple. They can't jump, either. If you use a battle droid, enemies won't attack you, (they'll think you're on their side) even if you attack them. (oddly enough)

Protocol/astromech droids
Protocol droids are droids made for translation, advice, and diplomacy, among other things. Astromech droids are droids that serve as mechanics. Neither have weapons. Both can open certain doors. The only difference is that astromech droids can hover and protocol droids can't even jump, and that astromech droids can temporarily disable droids.

Doors
Protocol and astromech droids can open certain doors, marked with the face of a droid. To open these doors, go in front of the terminal next to the door, and press X. After a few seconds, the door will open.

Hovering
Astromech droids can hover for a few seconds. Jump, but hold A, don't tap it. You'll hover until either: time runs out (you can only hover for a few seconds) or you let go of A.

Disabling droids
Astromech droids can also temporarily disable droids. Go up to a droid and press X to disable it.