IBM doesn’t seem to have any ready-made tutorial or introductory material for the High Level Assembler (HLASM) or Interactive Problem Control System (IPCS). Here is HLASM’s website. Clicking on the “Library” box on the left side of the page will bring you to the Assembler’s documentation. The IPCS manuals are in the z/OS information center for version 1.8 is here.
My advice would be to take an Assembler class from one of the several mainframe education vendors. If your company is a Share member you could also look for presentations at www.share.org. A Google search might also turn up some useful information.
Failing that, I would glom onto an old-timer at your shop (if you still have one) and find out what he or she knows. Even if this person can’t tell you much he or she may be able to point you to some Assembler exits or programs at your shop that you can study and recompile. I think it’s especially useful to look at the Assembler listing, making a careful study of the generated object code.
The old-timer may also be able to give you some advice on using IPCS. For self-training you should be able to use any of the plentiful system or SVC dumps in your system. And, by the way, disassembling the object code in dumps will only deepen your knowledge of Assembler and typical programming practices.
On a more general level, IBM has an eleven volume set of Red Books titled, “The ABC’s of z/OS Systems programming,” which I understand were specifically written for mainframe newbies. Here is the link to the Red Books.