When giving someone access to a folder in Microsoft Storage, consider what you want the person to be able to do with the content in the folder. You can allow people to edit or view the files in the folder. It is best to add people at the lowest permissions level that still allows them to do the work they need to do with those files.
Microsoft Storage uses waterfall permissions, that is, permissions that flow downhill and can only expand at lower levels. This means that collaborators will have the same permission level in subfolders as they do in the top folder. You can assign a given collaborator to a role with more permissions in folders deeper in your folder hierarchy. To do so, first invite the collaborator to the subfolder at the higher permission level, and then invite the collaborator to folders higher in the hierarchy at the more restrictive permission level. This will allow your collaborator to have different permissions at different levels of the folder structure.