Hello and welcome to the forum,
Start here (the Table of Contents of the JCL Reference):http://publibz.boulder.ibm.com/cgi-bin/ ... 0/CONTENTS
The flashlight/tubelight near the top left of that page is the Search feature.
Suggest you bookmark the ToC as you will use this manual often. Probably a good idea to download the manual as well to make it even more handy.