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.
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.
A junction box has several holes with removable plugs in the sides and back. Choose holes conveniently located for the cables you are splicing and remove the plugs. Have a cable clamp for each one and loosen the screws to open the collar. Pull about 8 to 10 inches of cable through the clamp and tighten the collar around it so it’s firmly held but not pinching the plastic.
A two wire cable run from a light fixture to a switch on a wall. Its only function is to control the on and off state of the light. Underground Feed cable used to run electricity underground. The sheathing on this cable is thicker and more durable than the NM cable used for interior applications.