Hi Roz,
Just to add a few comment to what Marc contributed:
sysout=* used to mean that the O/P for that DD is written to the same device that submitted the job. Usually a terminal. With the widespead use of spooling that may have changed.
If I may correct a minor point of Marc's, sysout classes don't define printers, they merely group the sysout. Usually tech support creates a variety of sysout writers that are "start"ed by OPS to create hard copy or disk resident archival copies. Some shops have 3rd Party packages that append delivery info to the sysout. Some sysout are held and never printed; they're just viewed from the Q they were assigned to, and eventually deleted.
All of these processing options must be identified and differentiated. So to determine which sysout is to get what processing, sysout classes are used to indicate the processing required.
Regards, Jack.