Lock trouble...please help!?

Question

i just got a new lock for my first year of high school

they are used with a key

i can unlock it easilly but i have no idea on how to lock it again once it is unlocked

(i cant pull the key out)

it looks like this

http://www.sentrysafetysupply.com/images/sentry-prod-images/AmerLock-1107BKA-1.jpg

but red

Answer 1

push the bar back into it, turn the key in the opposite direction and remove the key.