Knock out the spacer at the top of the frame and insert the sliding track into the cavity. Screw the track to the doorframe. Hammer two nails into the top of the doorframe upright and put the opposite frame upright in place. Use two nails to hold it in place.
In this video we are installing the door in an empty stud wall. If you already have plaster walls you are going to have to cut away the plaster. Place the frame into the stud wall. Make sure it is flush to the outside of the studs so that when you put the plaster on there is no bulging in the wall. Use the nail gun to fix it in place.
When fixing the other side to the frame make sure you position it 10mm in front of the stud so that when you put the plaster on it is flush with the edge of your frame.
Use your spirit level to make sure the edge of the frame is level. Pack the gap between the stud and the frame with Masonite packers. Nail it together. Make sure you have support at the top and bottom as well as through the middle.