Learn about IP Telephony

Before you get started, you need to learn about IP Telephony. Read this article about the Parts of a FreePBX System

Install FreePBX

Next, read the Installation Guide.

Finally, read about the First Steps After Installation.

You may also consider attending one of the official training courses, the Open Telephony Training Seminar. There are also other ways to get support.

Other Documentation Sources:

1. PBX Setup Guide
2. Voip-info wiki - Contains a lot of documentation about VoIP in general, as well as many Asterisk-specific things.
3. Asterisk Primer
4. Asterisk: The Complete Guide, 3d. Edition

Other Help Sources:

1. FreePBX Discussion Forums