a) what are the different ways to share files ?
b) How can I get list of file shares on Unix box in my company?
c) How can I get list of files and their content present on all the Unix File shares?
a) There are lots of ways, Samba and NFS are two popular ones.
b) Depends on your UNIX. UNIX file shares don't usually advertise themselves, so exploring is best done from the server side:
1) Find out what UNIX it has.
2) Find out what services it's running (again, depends on which UNIX). If any of them are nfs or samba, those are probably controlling the shares its exporting.
3) Find out where the configuration files for that service are kept (again, that depends on which UNIX).
Then you'll be able to see what their shares are by reading the configuration.
To list them, I recommend 'ls'.