Typically what you would do is:
1- Create user attributes to hold whatever data you want about users.
2- Create a user group
3- Set specific permissions for your content so that only members of that specific group can have reading access
4- Allow users to register an account. During the registration process, all the attributes you defined would be included to be filled up by the registrant.
5- Make the group you created the default group to put users in after registration

It all comes out of the box with Concrete5 except the last step but there is a free add-on in the marketplace that does just that