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 your desired Minecraft version

4. Click on Fabric

5. Click on Download. A jar file should be downloaded

6. Open MultiMC

7. Select Fabulously Optimized

8. Click on Instance Folder

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

10. Double-click on Fabulously Optimized. Minecraft should open up

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