Not really a stupid question. There are several ways of going about it:
a. The items are kept frozen until just prior to loading and then re-frozen on arrival.
b. Items requiring to remain frozen are packed in dry ice.
c. Large items can travel in a refrigerated container which is disconnected during flight but then started again once unloaded.
d. The good news is that most freighter types are bloody freezing the farther aft you walk from the flight deck.
e. Some items are so packed that they can remain outside a chilled environment for 48 hours.