The User Management app is free on the Appstore but you still need to purchase/add it to your Site. Once you have added it, it should be shown together with other apps when you go to the App Listing menu and choose Apps. Here you can activate the app and configure it to support external identity providers like Google, Facebook to allow your customers/users to login via Google or Facebook using Oauth Client ID/Secret provided by those providers to you (otherwise use SiteGUI keys). Your customers/users can also use email address/phone number to login.

Activating the User Management app also activates your customer portal at https://my.domain.zzz/account or https://subdomain.my.sitegui.co/account (free account), this portal will provide extra information for your customers such as order information, ticket tracker or other operations provided by Appstore apps.

If you have more than one sites and they are on the same servers, you may opt to use the User database of one site for another, basically sharing the same user base between the two sites. This works pretty well if your sites are related to each other. In order to enable this feature, you have to enable sharing staff database between the two sites as well. Click on App Listing, choose Site, then set the option "Use Staff Role From" to the site you want to use the Staff DB and enable "Also use User DB" to also use the User DB from that site.

Click on the New menu and choose User to create a new User account for your Customer. You can enter name, email, phone number and set the password, avatar image, status for your Customer account.

Click on the App Listing menu and choose Users to list all current users for your Site. You can edit each user account to change the user information, disable it temporarily or permanently delete it.