uh.....dont ask me for help cuz it can be really easy or very complicated if you don't follow the steps.
If you are unable to host and want to host....you have to port forward your modem. Find out what brand and model is your modem. Google "port forwarding the <whatever your modem model is>" Watch the youtube video how to do it. *look at the comments to make sure it is good vid how to do it.
For my modem, it was a simple "3 clicks and it's done" Dont worry about the DMZ and other things. Just 3 sets of numbers have to be entered if done manually. That is all.