The easiest way is to make sure you have the following settings under Settings > General
.
Under the Membership settings make sure
Anyone can register
is checked and New User Default Role
is set to subscriber.
This will allow people to register at example.com/wp-login.php?action=register
You can also use plugins like theme my login or Gravity Forms User registration (and I’m sure others) to make the sign up pages/process simpler.
I guess I’d have to know more about why you want to allow subscribers. If you wanted an even more limited role then subscibers provides you could create a new role via role scoper or the members plugin and assign that to new users.
However, if your goal is just to give users updates why not just provide them updates via email. There are a ton of plugins that do this. Automattic has one via jetpack or Subscribe2 is also an easy way to do this.