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.
There will probably be several options for an electrical source to serve a new outlet. For instance, it is likely there are several suitable wall receptacles in any given room to extend the circuit to another room or another floor of the house.
Adapters, like the one pictured, are available from hardware/home stores to make this type of installation. One of these may be required for light fixtures missing the necessary parts to fit the electrical box. For high ceilings, the threaded rod length can be adjusted to suit most situations.
Anything that resists electrical flow is an insulator. Insulators are needed in electrical circuits to contain the current flow and prevent shorts or electrocution. Vinyl plastic is used as an insulator for household electrical wires.