Spark has a link in the Help menu to a very old user guide in pdf format (www.igniterealtime.org/builds/spark/docs/spark_user_guide.pdf). Though many things in it are still true, but in some places Spark looks differently. It is also hard to update this guide (as it is in pdf format). Some features described in this guide do not work currently (voice chat) or will work differently in the current versions.
Ideally a wiki document should be created to replace this guide (copying most of its content), replacing some of the images and adding disclaimers about broken features. Then a link should be changed to that wiki document.