If you have a home network, you probably are connecting to the wrong IP.

Many routers do not have a loopback adaptor. What that means is that you cannot connect to your own links the same way somebody else can. Instead you must connect to your own network with your internal IP instead of your external one

For example.(The numbers are made up, but the situation is real)
you host the server for the world on your host computer, which uses your external IP for the program, which we'l say is 88.88.88.88.

Your host computer's internal IP is 192.168.1.5, while your router's IP is 192.168.1.1, your other computer's IP is 192.168.1.84

You need to direct your other computer to connect to 192.168.1.5 instead of 88.88.88.88 in order to connect to you minecraft server.

The one I run on one of my servers only has like 5 people that play actively atm D:

Are you trying to set up a LAN server for just the two of you? If so I can walk you through that process later.

I really only need like one for two people xD

If its just the two of you the process is quite easy

I just opened a server. Its new but i dont plan to keep it small and im still combing out the plugin bugs.

Server ip mc.demoncattribe.com

Try redownloading the server file from the site, it fixed my issue~ If the server is on the same pc your playing on then just use localhost as the address adn see if that works

I would host mine but my internet would be sluggish after adding more than 2 people XD