Zend certified PHP/Magento developer

Trying to host a game server on my raspberry pi – Security concerns & Static Routing

I am attempting to host a game server (Kerbal Space Program – Lunar Multiplayer Mod)
I know I need to somehow open a port – or something like that,

On my router all I have is:
“Static Routing”

And it asks for:
“Destination IP”
“Subnet Mask”
“Gateway IP”

I was reading and it seems like static routing is similar to port forwarding, I just dont know how to set it up or what to put as the above values.

Other thing is, if I set this up will it be a security risk for other devices on my network other than my pi?