you should put int he fridge and then in a cooler bag to bring home and then freeze/put in fridge (if to be consumed the next day). if you pump more than what baby is projected to drink the following day, take it as extra stash to be frozen for that rainy day.
dont't put in freezer at work since it may start to thaw on your way back. the idea is that the milk should move progressively to colder and colder temperature if it is to be stored. to reverse (cold to warmer) means you will be feeding baby the milk and it should not be returned to a lower temperature again
to thaw, leave in the fridge overnight. if not, set it at room temperature/in a bowl of tap water an hour or so before baby is to fed. breast milk thaws very quickly.