Measure the width inside of the doorway.
Cut the bifold door track equal to about 1/8 inch less than the door width. Mark the points with a pencil before cutting. Position the hacksaw on one side of the track where you have marked it for cutting. Move the saw slowly back and forth until the track is cut through.
Hold the track up to the doorway header about 1 inch from the front edge. Position the pivot bracket on the side the door opens, next to the jamb. Place the screws into the pre-drilled holes on the track and tighten.
Position the jamb bracket on the floor against the bottom of the door frame. Place the screws into the pre-drilled holes and tighten.
Push the top and bottom pivots into the pre-drilled holes on the doors. Tap the pivots into the holes with a hammer until they are secure.
Hold the doors upright. Slide the top pivot into the track pivot bracket. You may need to push down on the pivot to move the door into place. Slide the bottom pivot into the bracket on the floor.