System Recordings are usually necessary for any customizable application like voicemail greetings, or IVRs. To record a system recording the user must select the "System Recordings" link, either on a list on the left, or from the admin dropdown located on the top toolbar. Then the user will have to enter the extension number the user is going to record on. The web page has directions on how to record, listen, and save the recording.
Announcements fields specify where the system recordings are to be played. For instance, someone who is in a support queue and a sales queue, will get both support and sales calls. They may wish to get a notification depending on what kind of call is coming through. When they get a call, an announcement will specify "this is a sales call", or "this is a support call".
For the next chapter, see Chapter 8 - Music on Hold