Several things affect which interactions are recorded. This article outlines the things that affect recording: https://help.mypurecloud.com/articles/about-recording-in-purecloud/
Basically, you need to turn on line recording to record anything. I sometimes think of line recording as a very permissive DVR: once you turn it on, it records all external conversations unless you create policies that say to delete recordings under some conditions.
There are some exceptions (conversations between internal users aren't recorded), so check out the article for more info :)