You can give permission to access your new site to the same users who have access to this parent site, or you can give permission ...

You can give permission to access your new site to the same users who have access to this parent site, or you can give permission to a unique set of users.

Note: If you select Use same permissions as parent site, one set of user permissions is shared by both sites. Consequently, you cannot change user permissions on your new site unless you are an administrator of this parent site.