To Give access to the website or mobile app to a customer go to Customers -> Customers.

Once there, click on the icon  next to the client you want to give access.

Then go to Additional Information section, and within the section, to the User Access tab:

If the client doesn't have access to the web and to the mobile app already, the checkbox  "Have access to the web" won't be checked. To give him/her access, click Register customer in extranet. 

Once we have clicked, if the client didn't have an email account, the program will ask for it since it's necessary to give access, because the customer will get the password through that email account and also will use it as a username for both website and mobile app. 

If the customer's email was already on the customer's file you won't be asked for it. 

When the customer has access, you'll see the following:

As you can see, the "Have access to the web" box is checked.

And also you can send the user access information by e-mail (username and password), remove the access, reset the customer's password yourself,  and see the date of the last access to the web or the mobile app made with this user.

To manage all registered users at once, you can go to Website and Network / Registered Users. There you can send them a password reminder, reset their password directly, or remove the access