5.1 Normal General Overlays

#Which Overlays to put in this category? When to use this category?

As already said the category of general Overlays is for Overlays you only have once, not with different styles. Its the normal type of Overlays like a Settings Overlay which is only available in one color.

#How to put Overlays in this category?

Simple put all Overlays you want into a zip called YourThemeName_General.zip ---> YourThemeName = Name of your theme, like you defined in the strings.xml