How to allow visitors to register in WordPress

By default, only registered users with the necessary permissions can register new users. Only admins are allowed to register and manage users.

Visitors will not be able to get themselves registered. If you want to allow guest/visitors to register, you can do that by changing a single option in the admin panel.
Log in and go to Settings menu>General sub-menu.

On the page that open, under Membership, check on the box that says Anyone Can Register.
Underneath Membership is the New User Default Role. It will automatically be assigned to new users and set as Subscriber.
This role only allows users to register and manage their own account settings.
They will not be allowed to manage your site. After you’ve changed the settings on the General Settings screen, click on the Save Changes button.