Set-up: Find a pull-up bar, or another immovable graspable object. A barbell locked in place or sturdy desk may also suffice - simply make sure it is immovable and unbreakable, to bear your weight without incident. Face the bar or hold and grasp it with both hands, such that a line forms between the shoulders, the elbows and the apparatus.
Lift: Lift your feet off the ground and curl your legs and trunk up. Now pull yourself up until your chest touches the apparatus. Lower under control and repeat.