And how do I do that? It still doesnt work. Or should I restart my com and router first?
OK, so did you assign 192.168.1.100 to the MAC address of your machine you are on right now in your router?
If so you will need to release/renew the IP so it gets that IP, and from now one every time your PC requests a new IP from the DHCP server (the router) it will be assigned that exact IP.
Now, in port forwarding you want to add an application. Call it whatever you want. Then add the port, or port range. Then point it to the machine that you have set up with the static IP.
A reboot would refresh all network settings but may not be needed. ipconfig /release and then ipconfig /renew should do the trick from the command line.