This how-to is a step by step guide for setting up two gargoyle routers with a site to site configuration.
The server and client should not have identical LAN subnets, e.g.
VPN Server could have a 192.168.2.0/255.255.255.0
VPN Client could have 192.168.3.0/255.255.255.0
This applies for all routers/switches/firewalls in the VPN circuit
Your firewall/router needs to be configured to forward the correct port. The default port to forward is 1194. Forward this to your Gargoyle router WAN port. You might need to read your router manual on how to do this.
If you don't have a fixed IP from your ISP you will need to set-up a Dynamic DNS Services. see Dynamic DNS Services