What is the best way to rig a robot? So I already created a rig and everything for my Optimus Prime model but I'm not sure how to attach parts to this thing. I'm guessing I can't just parent every part, because I wanna make a transformation later on and parts need to move, rotate, etc... to other parts of his body and stick to that part from that point. 
The blue and red parts basically need to rotate in place (the wheels), or unattach from the part they're moving with, move to another part in some cool way, and then attach it there. Honestly I have no idea how to start with this parenting/constraints? so some help would be awesome!
Your question is a bit vague, but I think from whre you are you have 2 main solutions: either keep all these meshes as separate objects, or join them all into one object.
Separate objects : In this case, select the part, shift select the armature, switch it to Pose mode, select the right bone, and press CtrlP &gt; (Set Parent To) Bone.
One object: In this case, select the whole object, shift select the armature and press CtrlP &gt; (Set Parent To) With Empty Groups. Then you need to select each part of your object in Edit mode and assign it to the right vertex group (the one that has the name of the bone that is supposed to control it) in the Properties panel &gt; Object Data &gt; Vertex Groups.