You don't say what version of Word you're using, but you might try Insert -
Diagram - Venn diagram, which is designed to do precisely what you're
describing.
Otherwise, you can do it using Word drawing objects by making the circles
partially transparent. I find that 50% works well. Right-click the cirlcle
and choose Format AutoShape. In the Colors and Lines tab, set the
Transparency slider to 50%.
