Vector3 and Vector2 where would you use them and what is the difference.
The difference is that Vector3 is 3D (3 Dimensional) Vector2 is 2D, therefor you would use Vector3 with parts.
Vector3(x, y, z) Vector2(x, y)
Vector2s are 2 dimensional, and are used for advanced GUI work. AbsoluteSize, AbsolutePosition, et cetera, are all Vector2s. More information can be found here: http://wiki.roblox.com/index.php?title=Vector2