The tip-up is basically a spool on a stick holding a baited line suspended through a hole in the ice. When the bait — usually a minnow — is taken by a fish, the pull on the line releases a signal, such as a red flag.
A popular method to fish tip-ups is to set up a kilometer or two route scattering your tip-ups along the way. Most of the time people who ice fish this way put each line into a different depth of water at first then move the majority of their tip-ups to the depth that seems to be producing the best results. Give it a try!