Usually when people ask a question like this, it is for reasons of building an Umbraco site. You do not need, and should not use the actual Umbraco source code to help you build Umbraco sites. Start with the docs! https://docs.umbraco.com/umbraco-cms You might have GREAT other reasons though.. and please leave a note so we can help you navigate the codebase, which is quite extensive.