It depends of what you want to do. In most cases, I would recommend using and existing client/library, this would make the things more easy for you (don't have

It depends of what you want to do. In most cases, I would recommend using and existing client/library, this would make the things more easy for you (don't have to start from scratch, something already made in your favorite language). If you really insist in doing all by hand, you can start by checking compliance suits (XEP-0375) or https://xmpp.org/about/technology-overview.html https://xmpp.org/about/technology-overview.html. Those two links are actually at the top of the XEP list (https://xmpp.org/extensions/ https://xmpp.org/extensions/).