Once you've created your QuickSite, or while you are in the process of Editing it, click over to the Privacy icon in the right panel.
QuickSites have three Privacy Settings. You can make your QuickSite visible to anyone (Public), or limit it to authorized MediaSilo users that you assign as the Audience (Private). If you select Public with Password, you can create the password in the “Password” field.
If a QuickSite is Public, anyone with the url will be able to view the QuickSite. If the QuickSite is Public with Password, a password will be required before entering the QuickSite.
A Private QuickSite requires login with MediaSilo credentials of a user who has been listed as an Authorized User, in order for the QuickSite to be view.
You will be able to manage which of your internal users are Authorized Audience members in the Privacy panel on the right: