Hi,
Th instructions don't make sense to me in Exercise 3 (Example 3: Finding Distinct Objects Using the Power of One) of the Use Formula Fields module - https://trailhead.salesforce.com/en/trails/force_com_admin_intermediate/modules/point_click_business_logic/units/formula_fields?trailmix_creator_id=00550000006HirqAAC&trailmix_id=admin-exam.

It says to create a formula field on the User object for reporting the distinct number of unique users for opportunities. 

It goes on to instruct as folllows...
Create an Opportunities report and drag your Unique Users field onto the report from the left panel. You should see something similar to the following:


I don't understand how adding the Unique Users field to the user object would allow me to add that column on an opportunity record. It seems like the two objects would need to be joined. What am I missing?

Thanks,
Laura