How to allow visitors to register in WordPress
By default, in WordPress only a registered user with the necessary permissions to do so can register new users. From the default user roles that come preconfigured with WordPress only admins are allowed to register and manage users.
On the frontend of the site there's no option for visitors to register themselves. If you want to allow guests/visitors to register, you can do it by changing a single option in the admin panel. After you log in go to Settings menu>General sub-menu. On the page that opens find the option Membership and mark the checkbox Anyone can register. The option right under it is New User Default Role. That's the role that's automatically assigned to newly registered users. By default, it's set to Subscriber. This is a role that allows users only to register and manage their own account settings; it doesn't give any additional privileges in terms of managing your site.
If you allow guests to register be careful not to set the default role to one that gives more privileges to newly registered users. Otherwise you risk giving access to settings in your admin panel to anyone who registers.
After you change the setting on the General Settings screen in the admin panel don't forget to click on the Save Changes button.
For more information on users read the tutorial on how to manage registered users and user roles in WordPress. For more information on the general settings check out the tutorial on how to manage the general settings in WordPress.