Hello and welcome to the forum,
What "File handling" do you have in mind? Typically, a DCB is defined and then the file is opened, read or written, and then closed.
There is probably more assembler info at this link than you will ever want http://www-03.ibm.com/systems/z/os/zos/ ... pdf/#hlasm
The 2 main manuals you might want are the Language Reference and the Programming Guide.
If you are just beginning with assembler, you might look at:http://www.murach.com/books/mainframe.htm
There is an MVS Assembler Language book written by Kevin MqQuillen and Anne Prince that is very good for beginners.