Ekiga ships with a manual which is translated in nearly 20 languages. That manual will help you using and understanding Ekiga features. It explains simple things like account subscription or basic calling, but also advanced features like call forwarding, call transfer, ...
The Ekiga manual is reachable through the Help menu of the application.
The Ekiga community also maintains a WIKI. The WIKI contains different information from the manual like troubleshooting, a FAQ, a hardware compatibility list or even how to compile the software.
The Ekiga community wiki is reachable by following this link: http://wiki.ekiga.org.