How to add and manage registered users in WordPress
Registered users can contribute to your site and help you manage posts, pages, comments, etc. Registered users have access to some or all features of the admin panel, depending on the user role to which they belong. WordPress comes preconfigured with several user roles (administrator, editor, author, contributor, subscriber).
If you want to edit these preconfigured user roles or to add new ones, you'll have to use a suitable third party plugin such as User Role Editor or Advanced Access Manager because the default installation doesn't have such functionalities.
To add and manage registered users, log in to the admin panel and click on the Users tab on the left. On the page that opens you'll see a table with the existing users. The table consists of several columns providing the relevant information for each user (e.g. username, email, role, etc.).
You can remove some of the columns form the table or add them again. To do this click on the Screen Options button in the upper right corner and unmark/mark the respective checkboxes in the panel that appears. You can remove/add only the columns E-mail, Role and Posts. Using the Bulk Actions drop-down menu (above and below the table) you can delete more than one user at the same time. Just mark the checkboxes of the users you want to delete, select Delete from the drop-down menu and click on the Apply button next to it. Similarly, you can change the user role of more than one user simultaneously. Mark the checkboxes of the users, select the role from the drop-down menu Change role to that's above the table and click on the Change button next to it. When you hover the mouse pointer over a row in the table a couple of buttons will appear under the username: Delete and Edit. With them you can respectively delete only that particular user or go to the edit screen where you can edit the settings of the user's profile.
On the edit form you can change various settings related to the particular user. You can change the role to which the user belongs, the first and/or last name, the email associated with the user, the password and others.
To add a new user, after you click on the Users menu on the left click on one of the two Add New buttons, either the one in the left panel or the one above the table with the existing users. On the add form type a username, a password and an email in the respective fields, and select a user role from the Role drop-down menu. The rest of the settings are not required. After that click on the Add New User button at the bottom.
By default, new users can be registered only from the admin panel. If you want to allow guests to register from the frontend, go to Settings menu>General sub-menu in the admin panel and mark the checkbox next to Membership. Be careful with the default role that you give to new users. You can change it from the drop-down menu New User Default Role; it's below the membership option.
For some more details and screenshots read the tutorial on how to manage users and user roles in WordPress.