You must be trained before you use a respirator, but this is not the only time that training is required. If you use a respirator at work, you must be trained at least every 12 months.
Fit testing is required for all tight-fitting respirators, both supplied-air respirators and air-purifying respirators. The OSHA respiratory protection standard, 29CFR1910. 134, requires fit testing prior to initial use, when there are changes, and annually.