Put on heavy work gloves and walk to one side of the carpeted room. Grasp the edge of the carpet and pull it up from the underlying tack strip. Fold the carpet back by approximately 1 to 2 feet to provide room to install the baseboard.
Place 1/4-inch wooden shims onto the floor at 12-inch intervals and push them as far as possible against the wall.
Measure the length of the wall using a tape measure to determine how long the baseboard needs to be. Measure the same distance on a piece of the baseboard and mark it with a pencil.
Insert the baseboard into the miter box aligning the pencil mark with the 45-degree angle mark. Cut straight down using a miter saw to cut the proper angle. Cut the other end of the baseboard at a 45-degree angle facing the opposite direction.
Place the baseboard up to the wall, resting it on top of the wooden shims. Run a stud finder over the wall above the baseboard until a light appears, which is a wall stud. Insert 8 penny finishing nails into the baseboard every 16 inches which is the distance of the wall studs.
Fold the carpet back into place and tuck the edge near the wall under the baseboard using a carpet knife or a putty knife.
Repeat the process on the other three sides of the room to install the baseboards in the same manner.