just to start with ...
You can have zOS without CICS
You cannot have CICS without zOS
as a general point, CICS is seen by the zOS as a user program
( sophisticated and all, but still a user program )
When I tell somebody to RTFM or STFW I usually have the page open in another tab/window of my browser,
so that I am sure that the information requested can be reached with a very small effort