Starting with Sytist 0.7.8 is a paid access feature which means someone would have to pay to view a gallery. With this option enabled, when someone goes to view the gallery, they will be prompt that they need to purchase access. Once they do, then they will have access to view the gallery.
This option also allows you to automatically apply an account credit to their account for an amount you determine that can be used to purchase photos.
For this to work, in the password protect section when editing a page, it needs to be set to password protect.
You also have the option to manually assign people to the gallery at no charge or give someone the password where they can access the gallery at no charge.
The text shown on the paid access page is can be edited in the admin in the Site Design -> Page Text area.
Do NOT give out the password for a paid access gallery. Giving someone the password will let them access the gallery without purchasing access.
Do NOT give access to the gallery in the People tab. This will allow them to view the gallery without purchasing access.