Before setting up a Minecraft server with Fabric Mod loader, it may be a good idea to install Fabric in a MultiMc instance, download and test mods in that instance, and once you have everything set up and working, only then set up the server.

You can do that here.

Create a folder in any location in your computer that will be used by the server, for example c:\mc-server

Go to https://fabricmc.net/use/ and select the “Server” option, then download the Windows exe installer or the Universal JAR installer and save it in the folder you created, for example c:\mc-server

If you are going to use the latest version of Minecraft, go to https://www.minecraft.net/en-us/download/server/ and download the Minecraft server jar file. You must save it as server.jar in the folder you created, for example c:\mc-server