If you are using the holes in the back, push them into the proper holes until the clamp engages and locks them in place and there is no bare copper showing. Pull on each wire to be sure it is securely connected. Connect the ground wire to the grounding terminal on the device and any grounding terminals in the outlet box.
Or if you are using a receptacle on an upper floor to serve a new ceiling fixture below, it would have to be run through the soleplate and possibly some flooring, and into the ceiling cavity below. A switch loop will also have to be run from a wall location in the room below, to the new ceiling fixture.
When tapping an existing outlet box it will always be OK to extend the circuit from a box with fewer than the maximum wires running to it, as long as the total electrical draw from the other outlets in the circuit don’t exceed the ampere rating. To determine the load of the circuit, use the chart and formula for calculating existing load to extend a circuit at this link.
Use a drywall saw and knife to cut drywall and gypsum board plaster, use a reciprocating or keyhole saw to cut wood lath plaster. With the framing exposed, use a small saw to cut two vertical kerfs in the plate about an inch apart and then use a wood chisel to chip out a notch about ½inch or so deep, between the cuts.
Anything that will allow electricity to pass through it is a conductor. Metals are typically good conductors with copper being one of the best.
There are 3 basic types of wall switches you will encounter in most situations. A single-pole switch is the most common you will find and can be identified by two screw terminals, and in the case of new devices, a third one for ground.
Pry the molding off the wall working at each stud. Drive a broad chisel-type joint knife between the baseboard and wall. Pull out on the handle several times to loosen the molding enough to wedge a crowbar behind it.
Hold the fixture and splice the wires together, cap them with wire nuts and fold them up into the fixture box. Slide the base plate over the wires and thread the coupler nut onto the threaded rod to push the base plate up and hold it in place. Adjust the position of the base plate by turning the coupler until it’s snug against the ceiling.