Before proceeding, remove all wood shavings. Snake a generous length of speaker cable through the hole in the rear of the enclosure. Next, hook the speaker wire to the connector. Now mount your crossover devices, and wire the cables to the speakers. Covering the speakers with some type of grille may be a good idea depending on the location of the box in your vehicle.
Grilles are available from numerous sources, including speaker manufacturers.
Once your box is complete, the next step is to secure it in the vehicle. A careful inspection of the area surrounding the enclosure will help you determine the best and safest means for doing so. L-brackets usually suffice, or you can remove the drivers and bolt the box directly to the vehicle. If you choose the latter approach, be extremely careful when drilling holes. It's amazing how much damage can be done to a vehicle if you don't look where you're drilling.