This is a somewhat miscellaneous collection of essays of varying degrees of relevance:
Setting up UNIX really belongs in Section VIII of the UPM (it’s relevant);
The UNIX Time-sharing System is an updated version of the original “Communications of the ACM” paper. It should be re-read at least once per month;
UNIX for Beginners is useful if your UNIX experience is limited;
The tutorials on “C” and the editor, and the reference manuals for “C” and the assembler are highly useful unless you are completely expert;
The UNIX I/O System provides a good overview of many features of the operating system;
UNIX Summary provides a check list which will be useful in answering the question what does an operating system do?