init.ora

what is the function of the init.ora file and suppose by mistake it gets deleted , what will be the consequences on the server

The list of Oracle instances is in /etc/oratab. If you delete the init.ora for an Oracle instance, that instance will not start.
It is the parameter file for the Oracle database engine and can be found in subdirectory "..../<instancename>/pfile". Amongst the parameters is the location of the Control file for that instance.

Each init.ora file is a text file and you can read it with "more".