I want to edit a resource in a comparison and got this message - "A shared resource cannot be edited directly" - What does that mean?

You cannot edit resources that are used in another place in the Open Research Knowledge Graph, because any change of it would affect its representation in all these other places. In order to edit the resource, you have to visit the resource page (View > Resources) where you can also see all the statements that use this resource and which would be affected if you change it. However, if you want a resource with a different description or with new properties, you should create a new resource.