Hi @laurajcarrion ...
Sorry to see that this question has been sitting out here in the Community for so long without a reply. As far as I can tell, there really isn't a screen within Commons (from an admin perspective) that has Commons permissions for users. There is an "Admin" screen where you can configure things about what kind of content can be shared, but nothing really about user permissions. There is an area to create Groups and Consortiums ... which you can read more about here:
Out of curiosity, what kinds of permissions are you wanting for Commons? Would be interested in hearing more about this. Thanks. Take care...be well.