MCA Suite allows Deals to be assigned to two (2) system users. To assign a system user to a deal, create a Deal and go to the "Assigned To" and "2nd Assigned To" fields.
Both fields performs a lookup against the MCA Suite system user list which allows you to select the right user (agent) to be assigned to the deal.
You can also have Deals assigned to a "Team" if you have that setup in your tenant. Here's an article on more deals around Teams.
This field is optional and does not need to be filled out.