Access to internal network

have network topology: internet>>>>Router(configured with static ip)>>>>> fortigate firewall(connectivity with some ip range will be needed)>>>>>>switch>>>vpn server... so really want to know how my users who will have to dial static/live ip to get access to server...how my vpn server will reachable..? I want to create  access vpn on vpn server so my remote user can access remotely..My static ip is configured on router facing internet..after that there is hardware firewall as mentioned.. and beyond firewall there is my private network on which server exists... suppose IP address of my vpn server is 192.168.1.100 and my live/static ip is :1.2.3.4. and one more IP subnet for connectivity of firewall and router or it is not needed... finally i will have to configure port forwarding  to my server...on router.... on firewall...where and how...?