Sconce Installation Help (Wiring)

Okay. This is my second time installing a light fixture in my house. First time was super straight forward (connect the black white and ground wires and wrap the ground wire around the screw on the plate). This light fixture is stumping me for some reason. The ground wire isn’t in the same spot as the white and black wires and there’s no mounting plate. I just can’t figure out what to do with the ground wire (which I’m assuming is that yellow wire) and the instructions are totally useless. Also unsure what to do with that white box (seems like it’s used to replace the twist wire connectors but what is the black piece for and the box part to the left of the wire connectors). Any help would be greatly appreciated (also I’m highly aware that I should probably have a professional do this, but I really don’t have the money for that at the moment and think I can relationally do it myself).