Parenting separate objects to the same armature

Question Rigging

Hi there! I am attempting to make a robot character guy and rig him. I am very new to rigging. How do I parent each bone to that specific and separate object I want it to effect? Example: I am trying to parent the "arm_upper_Left" OBJECT to the "arm_upper_Left" BONE? Do I have to join all the objects together so that it's "one mesh" then click mesh then click armature cmd+P parent with automatic weights at that point? The reason this is important is that I have designed the joints to already be able to bend at the proper robot joint using the 3D curser to get it right where I wanted the origin point. So I know I want that bone to 100% only cover that one object and effect it only at its rotation point. I have ALSO very carefully placed the head of each bone that will be at the rotation points to be at the exact origin of the joint portion of that object. 

I hope this makes sense! I am trying to make him the right way but I have a lot of random holes in my understanding.