What distro/version are you using on the Pi.
It should be just like adding any other Linux computer to a Windows network: Use Samba. The Arch Wiki would be a good start:
https://wiki.archlinux.org/index.php/Samba
Please note that the Windows Homegroup thingee (is that still a thing?) works only with other Windows devices. To make Windows shares visible to non-Windows machines, you have to use what Windows misleading refers to as "simple sharing."