Minecraft Server 25565 Port Failure?

I'm trying to create a Minecraft Server, but with no success. I'm using BT internet and put my port in, however whenever I check my port it says that it is 'closed'.

What dpes this means and what do I do? Please give me some step to step instructions - i've been trying for a while now.

PS. If you need any extra info i'll be happy to tell you like firewalls etc

Added (1). How do I open the port in the firewall of the server and where do I locate the firewall?

Added (2). Also when I try use this server I get a java.net error. What does this mean?

Added (3). I opened the port in my firewall… Still doesn't work.

Guest

You need to open that port in the firewall of the server. You should then be able to access it by its internal private IP address form your network. That has NOTHING to do with the router. You can't access your external router public address from inside the network and expect to connect to it. For someone outside to connect there are already games ports available in the games section of the router firewall and you need to point one of those at your server

Fred