how do you share a photo album in family sharing?

When you enable Family Sharing, you will automatically have a shared family album. To fill this album, select photos and use the Share button to share the selected photos in the shared family album. How to share albums in Photos on your iPhone, iPad, and Mac - Apple Support

• Select the photos in Photos, click "Share", select Shared Album, then select "Family".
• All family Members should enable "Shared Albums" in the Settings > Photos > iCloud.

If you upgrade to iOS 16, you can share directly a Shared iCloud Photos Library instead of a single Family Album. iOS 16 - New Features - Apple