[Koha-devel] how to start customization

Hello every body, I have got the clone of koha using the Git after configuring the koha on Debian 4.0. Kindly let me know how can I set development environment to customize koha according to the requirement of our own library. Clone of koha on my local system has all the code of koha modules. Should I access those modules and make changes in required and after saving that locally should commit it using Git? Please help me as I am new entrant in Perl and koha. Have a nice time and thanks in advance.