I need something to rig a hand, just a hand not a whole arm, so I found this tool, but I am not sure if it could rig just the hand for me, or it only works for full body meshes. Anyone knows how to use it?
You can use Rigify: add an human metarig, delete in edit mode all bones except arm, forearm, hand, fingers.
Then set all bones in the appropriate location.
Back in object mode click the create rig button, hide the metarig, in edit mode enable all bone layers and select and delete all bones relative to arm and forearm.
A couple of little bones are unselectable, so you'll have to toggle the selectability arrow in the outliner and toggle their selectability property.
You can also delete root bone, if unnecessary.