Helping hands may be helpful when soldering. If you have never soldered before, check out this soldering technique guide.

Slide the red wire through the hole of the terminal that corresponds to the right speaker. Wrap the wire around the terminal a few times, then solder it in place.

Repeat this step for the terminal that corresponds to the left speaker. Note that the left audio wire is often white or green.

Finally, solder the common/ground wire (often copper colored) and any multicolored wires through the remaining hole.

The pictures show a blue wire and several yellow wires. The blue wire was soldered with the ground wire, and the yellow wires turned out simply to be nylon (not actual wires).