Choose the spigot lock you want. These are made to fit a variety of spigot sizes and come in different materials to match the plumbing fixtures you have.
Purchase the spigot that meets your design needs.
Remove the components from the package. You should have the round coupling that has a rubber diaphragm on the inside with a revolving tang on one end, a sleeve that sits over it, and the lock. (Some locks have the sleeve and lock as one unit, others may use an third-party pad lock to lock it.)
Twist the coupling over the spigot. You don't need to tighten it with a wrench, simply doing it firmly by hand is adequate. The revolving tang should be on the opposite end of the spigot and able to freely rotate.
Place the sleeve over the coupling so the locking unit is away from the spigot attachment.
Attach the lock, or twist the key to lock the unit.