There are two four-letter words that you may notice get used a lot when talking about Zephyr. One of these, zctl, has appeared in this document many times already, as part of the commands to change Zephyr subscriptions, Zephyr exposure levels, and other things. The other one is zwgc. In this section, both the zwgc and zctl programs will be introduced, so that you can better understand how Zephyr actually works.