if you are trying to join on the same network as the host (both computers are in the same house), you must use the servers "local" IP, instead of the public IP the server gives you. If you don't know how to find your local IP, tell me your OS (windows, linux, mac, etc...) and I'll guide you through it.
could you help me sir my computer is a windows and litterly couldnt join any game why did i call you a sir
If you have a windows computer you should type in the start menu, "cmd" without quotes, then you need select the first result, lastly you need to type in the box that comes up "ipconfig" without quotes. Your local IP should be to the right of "IPv4 Address." for example "192.168.254.57"
and you called me a sir because I am one.