Installation Guide

One of the many ways to install ejabberd is using the binary installers for Windows, Linux or Mac. This video is old, for Linux, but it is still valid for current versions and Windows.
http://www.process-one.net/tutorials/ejabberd_setup_linux_en_viewlet_swf...

For learning purposes, you should experiment using a well known and good Jabber client, like Psi, Gajim, Jabbim, or Tkabber.

BTW: if you are new to Jabber and ejabberd, try to learn slowly, one thing at a time, because there are many new concepts and you could get a headache. Try also to learn from your own experience, from the ejabberd Guide, http://xmpp.org/protocols/ ...

The default configuration has In-Band Registration enabled, so anybody can register accounts using his Jabber client. You may want to disable this in a corporate server.

The admin (you), can also register accounts using the WebAdmin, or Ad-hoc commands, or sending XMPP stanzas, or in the shell console using ejabberdctl. You can also install other modules that allow to register accounts using XML-RPC (ejabberd_xmlrpc), REST calls (mod_rest). Also mod_register_web provides a web page where your users can create accounts.

Yes, using some of the methods mentioned before.

You can use whatever library or client you want, as long as it's XMPP compliant. That library seems to be correct for the task.

During installation, you can specify the Jabber domain you want to use for your Jabber server. If you only want to test, you can set "localhost". If you want it for your local network, call it "mymachinewhatever". If you want it to be accesed from Internet, you will have to call it "mycompany.com" or whatever.

Then tell the Jabber client the username and the server (the Jabber domain).