How to get Oracle_Home directory?
Place your tnsnames.ora in a directory of your choice, then set the TNS_ADMIN environment variable.


Open CMD, enter sysdm.cpl
In the Advanced tab, select Environment Variables
Under "System Variables", click on 'New' and enter TNS_ADMIN as the name, and the path where your TNSNAMES.ORA resides as your value


Windows steps from here.

On Linux, it's as easy as setting the variable in your shell startup script, eg .bashrc:

export TNS_ADMIN=/path/to/instant/client