How to connect iMac to Windows Pc using file sharing

I have 21.5 iMac Retina (3 months old) Os High Sierra.

I have used the Sharing app to allow others to share some of my folders.

How how do I set up sharing files with my wife's Windows 10 PC?

They share the same wifi network but I cannot work out how either machine can see the shared folders.

Can someone help me please? (I used to be ok at the networking with Windows)

thanks

Baz