A triple Venn diagram shows how three groups overlap: seven regions, from “only A” to the center where all three meet. Type into each region, or paste three lists and let the tool sort them.
With three sets A, B and C there are seven places an item can go: only A, only B, only C, A and B (not C), A and C (not B), B and C (not A), and the center, which belongs to all three. The boxes on the left follow that order and are labeled with your circle names, so you always know which region you're typing into.
If sorting items into seven regions by hand is the hard part, use Paste lists instead: one list per circle, one item per line, and the tool places every item in the right region.