Forge is used for modded servers, here's how to install it:
1) Go to here and download the Installer version of the version of Forge that you want.
2) Run the file that you downloaded and then select Install Server. Change the place it installs to by hitting the '...' and install it to an empty folder.
4) Go to the folder and rename the Forge jar file to custom.jar. 5) Upload everything (including the libraries folder) to your server's jar folder, then select custom jar in your server's panel. 6) Save and start your server!
