Warn everyone in the building that you will be testing the alarm system so they don't think there is an actual fire.
Pull the alarm(s) as you would if there were an actual fire. Most alarms have a diagram pictured on them that shows which way to pull the lever to activate the alarm. Pull until you cannot pull the lever down any further.
Ensure that the alarm tone sounds when you pull the lever. If it doesn't, the alarm is not functioning properly and should be repaired or replaced.
Turn all alarms off to end the test by flipping the main switch for the system, usually located in the breaker room of the building.