Finding a 2.5mm Male Jack with a good length of wire on it is very important to this project.
If you look at the wire you'll notice that there are in fact two wires hooked together. One is all black, and one has a white strip along it. The all black wire is Positive, and the white strip wire is Negative.
You'll first want to use some scissors or wire cutters to split apart the two wires. Just a little bit. Don't pull them apart too much, as this makes things more difficult later on.
Then use some wire strippers to strip the plastic coating off of them.