Supplies you need are:

First You need to remove the Plugs from the end of the light fixture or outlet you wish to extend and straighten the wires like this:

Cut the wire (From your extra wire roll) to a length you need so you can attach it to the end of your fixture and strip the outer part off to expose the wire like this:

Next you would twist these pieces together like this:

On a Toothpick, take a small dab of Rosin soldering flux and smear it on these exposed wires:

Take your hot soldering iron and melt a little "soldering wire" on the tip of your Iron:

Touch the exposed exlectrical wires with the tip of your soldering iron to melt the "soldering wire" over the exposed electrical wire and it will look like this: