Written by: Bagel
Creating a modded forge server is easy: to start, go to freeminecrafthost.com and click play now. Then go to create server. Enter the name of your new server and choose the “Forge” egg.
After that, enter your other server choices and click “Create server”. Find your server in the dashboard and click “Use Server” to enter the control panel. Go to startup and enter the forge version you're going to use. To find this, go to https://files.minecraftforge.net/net/minecraftforge/forge/ and choose your server version. There will be a box that says “Download Latest” or “Download Recommended”.
We will not be downloading any forge files in this guide. Instead we will copy the server version number (in this case 1.21.1 - 52.0.2.) and paste it in the forge version box on the control panel. Remember to remove any spaces in the version number, otherwise the server cannot recognize it. After all that, hit start on the server console and you're almost done! The server will take a little while to start up, but after everything's set up and running, you can put all of your desired mods into the “mods” folder in the file manager. After putting all your mods in the folder, restart the server for them to work. Make sure you have the mod installed on your client before you join, and you're good to go!