How to take backup of a oracle schema

You can use Export/Import OR Data pump.

For export(this command can be used to generate a backup file on the client machine)

exp user/password@database owner=user file=datafile.dmp log=logfile.log

where

database=db entry from tnsnames.ora,user=user-id to connect with,

password=password of the user connected with, 

owner=schema which needs to be exported,

more options can be expplored by

exp help=y