Wix will let you create password only pages, however it is a general password only and can’t be different for each user. When a user signs up to be a site member, then they can create their own unique password.
For your user, you will have to create a password and tie it to that specific member either through their userid or email for example, so that when they use the password on your site you can simply query your members dataset and get their info from the members row that matches the given password.
Otherwise, if you wanted to use the simple password protected pages within Wix settings, then you would have to create a separate page for each and every user, so that only they have the correct password for that page.