Do I need to register my work somewhere for the license to apply?

Copyright in most jurisdictions arises automatically when a work is fixed in a medium (written down, recorded, saved). You don't need to register it anywhere.

Likewise, a Creative Commons license attaches to a work as soon as you, the copyright holder, label the work clearly with that license. Registering an entry in the CommonContent catalog doesn't grant any new legal weight — it just makes the work findable.

That said, in some countries (notably the United States) registering your copyright with the government office unlocks stronger remedies in court. CC licenses do not replace that — they sit on top of whatever copyright system you already have.