Ok, I see what you mean now. The "Web Part Tools" tab is provided by the SharePoint infrastructure as part of a web part - this is not something that is specific to the Map Web Part. Functionality specific to the Map Web Part is grouped under the "ArcGIS Map Web Part" tab. So the "Insert Related List" button on the ribbon does not work with the Map Web Part.
Join functionality of the sort you're asking for is not there in the current version of the software, but it is something that we are considering for a future release. It may be, however, that this functionality will only support one-to-one relationships to begin with.