TABLE FILE TEST
PRINT
*
ON TABLE HOLD AS xxx
END

If the o/p is stored in hold file, will it get stored to disk or will it be available in the memory? What document will give me this kind of information?

WebFocus hold and save files of any format are stored to disk, never to memory.
By default they go into the TSnnnnnn sub-directory to edatemp on the server.
To force them to another location you must filedef the file to the place you want such as

FILEDEF HOLD DISK c:\temp\hold.ftm
-RUN

You will have to copy or move your master as it will disapear at the end of the job.

It's all documented in

Creating Reports With WebFOCUS Language DN4500580.0904 W.ich can be downloaded via the Focal point documentation link.

If multiple users are accessing the procedure which is having intermediate files, will it get overwritten?

You only need to use FILEDEF is you want to permanently keep the file.
If the files are only work files intended to exist only for the length of the request, then WebFocus does a dynamic FILEDEF to the working directory.
Every time that a user starts a job on WebFocus it creates a new working directory for the task dynamically under edatemp and so every user has a unique environment and there is no risk of picking up or overwriting other users work files.

If you use manual FILEDEF to a fixed location then the files will be overwritten.