Blocks are the shapes we use, without them we can't build anything. Blocks can be resized, rotated, colored, and can be added with a texture. The game is all about blocks, building, and you can see it in the game's name. There are many different block shapes like: Square, Triangle, Pyramid, Hepta, Tetra, etc.
Props are blocks made by the game developers, some can be resized while some can't be resized. These are complex blocks which can't be made perfectly with the blocks we use to build. Props include: flower, tree, bush, table, chair, laptop, etc.
Gears are equipment used by blocksters, these are one of the special kinds of blocks, they aren't usually "blocks", they can't be resized. These gears can be used on other creations, not just blocksters. Some gears have their own action. Gears include: Swords, Guns, Melee, Hats, Helmets, etc.
Action blocks are no ordinary blocks. These blocks are the key to make your creations to life. It can/must be scripted by the player itself for it to move. Action blocks can/can't be resized. Most action blocks can't be resized. Some of it can only be resized on one direction only, while some have limitations. Action blocks include: Tires, Rocket boosters, Gravity blocks, Connectors, Rotators, Motors, etc.
Blocksters are your character, they are equipped with gears, clothing, and colors. Blocksters can't be resized, there are two types of blocksters, blocksters and mini blocksters. The blockster is one and a half blocks tall when played. All gear fit it because it was the only character used until one update. The mini blockster is almost the same height but smalle. Some of the gears can't be used on it because it was recently added but the game might also add gears for the mini blocksters, like a backpack.