To starting hacking into ERPNext, you must have some understanding of how a dynamic web application works. There are hundreds of architectures and frameworks to make web development easier, but at the core there are a few elements that are important to understand.
ERPNext is built on `wnframework` which is primarily developed for ERPNext but can be extended to make similar database driven applications. wnframework uses Python on the server-side and has a javascript based client for entering data, managing workflow and making reports.