In my experience with spell tags (and skill tags, if you are using those, as well), you will receive a small piece of paper at Logistics check-in each day for all o the spells available to you. Each time you cast a spell (which consists of holding a "packet", touching it to your target and saying your incant, or saying the incant then throwing it at your target), you will tear off the "Unused" flag at the bottom of the spell tag. In the heat of combat, you are not expected to stop and fiddle with your tags; but you should tear off "Unused" flags at your earliest convenience. At the end of a mod or scene, a Marshal may also ask to collect all used tags from that module. Alliance Denver may run things a little differently, but that should give you a general idea to start with.
-Luke