When a custom report is shared with you, you can communicate directly with the report's creator via the Analytics Suite solution, so that you may ask questions about a particular analysis. To do this, click on the paper plane icon in the blue banner.
Once you've clicked the icon, a window will open allowing you to write a message to the report's creator. Click on "Flag" to send the message.
The report owner will receive q notification when s/he logs in to the Analytics Suite homepage (1) and will have access to the message by clicking on "See more" (2).
Once the report owner opens the message, s/he will be able to open the report to the exact analysis in question.