Other computers can't connect to my server

Solution 1:

Sounds like you have not port-forwarded your router.

This guide is for a much older version of Minecraft, but the port-forwarding portion is still good. Follow the guide thoroughly.

https://portforward.com/softwareguides/minecraft/portforward-minecraft.htm

If you're in a situation where you're unable to port-forward (living on a University Campus, or otherwise unable to access the router configuration), you can look into a Virtual Private Network program, such as Hamachi.

Be warned that Hamachi modifies your network adapter to work, meaning you'll need some networking know-how to fix things if something breaks.