The hazard
Machines can start up without warning, and stored energy can be released even after the power is off. Lockout tagout keeps a machine from moving or releasing energy while someone is working on it. It only works when everyone follows the same steps, every time.
The action
A tag is a warning device. It does not physically hold a switch or valve off the way a lock does. A tag must never be removed without permission from the person responsible for it, and it must never be bypassed or ignored. If you find a lock or tag, leave it alone, never try to start the equipment, and find out who owns it. (29 CFR 1910.147(c)(7)(ii))
ASK THE CREW
Who on this crew is authorized to lock out, and who is affected?
From the talk: Lockout/tagout (LOTO). Read it in full, free, with the questions and the sign-in sheet.