The leg at the bottom of the bed includes a folding mechanism which allows it to be moved as needed for use or storage. It's a handy feature, but in order to protect this part from slipping when an accidental kick or toe stub strikes, a locking feature is included to protect against any unwelcome movement. Part of "making the bed" will involve flipping a switch along the metal frame at the foot of the bed. To lock or unlock the leg latch, simply lift the lever and flip it in the opposite direction.
When the bed is closed, the leg is stored by folding up, in, and around the mattress. When it's time to open the bed for use, the leg is unfolded, positioned on the floor and locked into place.