I want to make few changes in the source code and use the software. Whats the process for the same?
Do you mean legally or technically?
Legally, it’s under the GPL license, so feel free to change what you like. If you sell it, the recipient gets the same freedom.
Technically, it’s best to have a look into the extensive Wiki docs. Since it’s php and not e.g. Java, there is no “build” process.
could refer me some docs for technica installation
Please check the wiki.dolibarr.org under developer documentation. PHP is a interpreted language so no need to rebuild anything. Just install, change and try.