Hello @Peggy Byrne !
Pipedrive has a duplicate detection system to help users avoid creating multiple entries for the same People or Organizations. That's why when you enter data manually sometimes you get pop-up suggesting a contact that already exists. There are is duplicate detection rule for Deals, though. Learn more here: How does the Merge Duplicates feature identify duplicates in Pipedrive?
If, however, you still spot duplicates that you want to merge, there's two ways you can do it:
Hope that helps!