MultiMC

1. Find the mod or mods you want to add from the list of Fabric mods on Modrinth

2. Click on the mod's Details page

3. Click on Download next to the latest version compatible with Fabric and Minecraft. A jar file should be downloaded

4. Open MultiMC

5. Select the FO instance

6. Click on Instance Folder

7. Copy the jar file you downloaded in step 3 to the mods folder

8. Launch the instance. Minecraft should open up

9. If you can see the newly installed content in the Mod Menu, you're done!