Gmod Port Forwarding

I was trying to port forward my sandbox server and i dont know how to do this. The video's i watched were all other Setups. I have frontier and this is what i do. I click Port forwarding, Click Add, Under select a Existing Service/Rule i click create (i looked for existing services, and i found Counter strike and HL2. I dont know if those work). next=
Protocol=Tcp,udp,or both
GlobalPortStart=idk
Globalportend=Idk
Basehostport=idk.

Clueless and i have been trying for hours.