You can access the Partner Detail Page by heading to your Partners page (via the top menu) and clicking on the name of any individual partner.
The page itself provides you with a few different things:
A count of how many overlaps exist between each of your populations and each of your partner's populations. An overall view is available in the "Top Overlaps" chart, then there is a "Population Breakdown" that shows you totals per you partner's population.
The "Population Breakdown" is organized by your partner's populations, and under each population name is a list of all of your populations and a count of of how many overlaps exist in that particular combination. A bar graph on the right side of the page illustrates the magnitude of this overlap relative to its intersection with your other populations.
Clicking View Details will take you to the Compare page, with you partner's population selected and all of your populations selected.
Shared with you and Sharing Settings
Learn all about managing sharing data with your partner here.