Basically, your door is 2 halves that sandwich the wall. To start, all you need to do is remove the pre-applied casing/trim from the half of the door that actually has the door on it (the other half is basically just trim). You can usually bump this off fairly easy. After that, just watch our interior door install video, as the procedure will be the same. After you complete the video instructions, simply move to the otherside (backside of wall) and push the remaining door half (mostly just trim) into the installed half. Nail a couple nails through and reinstall the trim that you removed in the beginning.