I personally don't like port checker websites. I have seen too many false negatives. I prefer testing with a cell phone or a buddy.
1. Test your server from inside your network. This would mean connecting to it from another computer at your home or a cell phone on the WiFi (yes, I'm assuming you have another computer or WiFi). If it works, great ... if not, then we have problems other than port forwarding. So, get that server working!
2. Test your server from outside your network. Take your phone off WiFi or call a buddy (sorry, txt a buddy ... who calls anymore?). If you can't connect then your port forwarding is messed up (slight chance of firewall on the computer stopping the connection, but I don't see that too often)...