Does anyone know a fix for this?

I can't get my external extensions working. It says the manifest is missing, but it is there!

IMPORTANT! The extensions listed below were found in the extensions folder but are not available for install or upgrade because the errors displayed below were detected.
Loading of extension "y_repository" failed.

Missing manifest.xml.

What the title says, I like to make plugins for stuff. I saw this forum software, and it reminds me a lot of my favorite forum software but this is free. So I have decided to use it, however I don't know how to make extensions. Can someone please tell me how thank you.