port forward, if you dont know how to do so just look below
>>start game>>(gamemode)>>click advanced after you click your gamemode>>
in advanced the first thing that is there is "port", for instance mine is set to 38000, i really don't know what works for you or other players for that matter so just set it to 48000 or some other number, just keep trying until you get a good one i guess
what
You can try every single port but if you don't open it in your router none of them will work
Press the windows key and R at the same time. In the window that pops up, type cmd and press enter
In the black window that pops up type ipconfig, now look at the default gateway, it'll probably be something resembling 192.168.1.1 or something, type that in your browser adress bar
Now log in to your router on the page you just ended up on in your browser. If you or your parents never changed the password or username, both of those are probably 'admin'. Now I can't help you any further because its dependant on what brand router you have, but usually there will be a port forwarding option under network somewhere. Open port 28000 on both TCP and UPD for your PCs local IP adress (probably something like 192.168.1.5 or something, its also in that ipconfig window somewhere). Now your server should be port forwarded.