Creating separate network for server

I've been trying to set up a separate network for my server to isolate it from the rest of my network since it will be exposed to the internet. I cannot wrap my head around how to get it set up.

I want to create a network (192.168.4.1) that uses the 4th ethernet port on my router, and assigns the server with a static IP (192.168.4.2) and is able to access the internet. Any help is greatly appreciative.

If your device uses DSA, parts of the instruction could be outdated.

My device uses DSA, is there anywhere with updated documentation?