Lock the garage door.
Screw garage door closed with drill from interior. Screw through the lip on the side of the door into the studs that frame the door.
Measure the dimensions of the door frame and build a stud wall on the ground to match these dimensions using the 2-by-4 lumber, screws and drill. When placing the studs, space them 16 inches apart from one another.
Cover one side of the constructed stud wall with vapor barrier using the staple gun and lift the wall off of the floor into the recess of the door opening.
Screw the base plate to the concrete below using the concrete anchors.
Screw the stud wall frame to the door frame in the same manner that the door was closed with.
Caulk between the stud wall and door frame as well as base plate and concrete to ensure a tight seal.
Insulate the stud wall with R13 by cutting the insulation to fit in between the studs and stapling into place.
The wall is now ready for finishing with sheet rock, plaster, paneling or whatever you desire.