Direct link web tabs
There is a new type of web tab available in Portal Access: direct links. When you create a direct link web tab, it generates a URL with a direct link to that object, like a Presenter Report, Data Discovery Dashboard, or Rapid Report. The URL has the Sales Portal navigation bar disabled so when you send someone that URL, they can access only that tab and nothing else.
To learn how to set up a direct link, read: Adding web tabs.