Sending an email to everyone with a certain role
If all you want to do is send emails to users of a certain role, you can use the Mass Contact module.  It enables a user to send an email to users by role or taxonomy. It is very easy to use, without any coding knowledge necessary. I have used it on a couple of business-related sites.

The other alternative is to use Simplenews. This is used mostly for sending email newsletters to lists of subscribers, if that is the kind of email you want to send.

But if you really want to use rules, I suggest you go through some documentation like this. Under the "Add a new action" of your rule, under the "System" section, there is a "Send email to all users of a role" action. That may be what you need.