Having been lucky enough to be an Excel Trainer for many years, I can't believe I forgot how to do this and had to look it up!
I was tracking how many different times people attended training, but I wanted Excel to tell me how many people were unique and give a count for each person.
It is under Data - Sort and Filter - Advanced.
Then I had it copy the data to another row and only show unique values. Then I ran a count of the names, and it was done!