This is presently a work in progress. Until it's written, you should start here: http://www.freepbx.org/support/documentation/installation/first-steps-after-installation Other Documentation Sources:

• Elastix Without Tears
• PBX In A Flash Without Tears
• PBX In A Flash For Dummies
• PBX In A Flash Documentation
• NerdVittles.com
• PBX Setup Guide
• Voip-info wiki - Contains a lot of documentation about VoIP in general, as well as many Asterisk-specific things.
• Asterisk Primer
• Asterisk: The Definitive Guide, 3d. Edition

Other Help Sources:

• FreePBX Discussion Forums
• DSL Reports VOIP Tech Chat Forum
• PBX In A Flash Forums