i have downloaded the Minecraft rig from this website: http://www.rymdnisse.net/download/blender-rigs/minecraft-blender-rig/ ,but for some reason, when i move the body around, the fingers streach out. how can i stop this?
this is most likely because you're currently selecting the mesh/skin when trying to move the character.
Instead you need to select those bones in order to move/rotate/scale the character.
This tutorial might help, https://youtu.be/_C3CCz5S75A?t=7m56s (at 7:56) To move the whole character in while in pose mode, select and move that larger platform around his feet.