Why can't I open port for my Minecraft server?

I've tried to port forward a lot, and I think I've done it right, I've also used the Simple Port Forwarding application, but after I test, it always says that the port isn't open, some said I should use:25565 after my server IP, i did so, but there was no luck. So how do I open port?

In addition to port forwarding, you need to open the port in your firewall as well. Windows has a firewall that is enabled by default. Either disable that firewall, or edit the firewall to allow the port.