The FreePBX DHCP Server provides a simple and integrated, way of configuring clients of a FreePBX machine.
A machine that is going to act as a DHCP server must have a the FreePBX Firewall correctly configured, with an 'Internet' interface, and a 'Local' interface.
Make sure that the Local interface does NOT have a default gateway - this machine IS the default gateway for the Local network!
Enable DHCP Server
In the DHCP Server setting, enable DHCP on the Local network
Configure DHCP Server
After it is enabled, if you need to change any settings (Note that these are automatically configured and it is extremely unlikely that you will need to change them), this can be done by clicking on the 'Manage' button