Log into your Doodle account and under your name go to your account settings. Under the Premium Doodle-tab you will find a User management section. There you can enter the desired e-mail addresses or e-mail domains.
If some on your users do not already have a Doodle account, they need to start one. You can send them this link to get them started.
Ask all your users to log into their Doodle account and check that they have been added to the Premium subscription. They can open the following page (it's in their account settings): http://www.doodle.com/settings/premium
The pull down underneath "Your Premium Plan" should be set to the name of the Premium account holder. In case "Do not use Premium Doodle" is selected, simply shift to the correct subscription. Your users now have access to the benefits of your Premium subscription 🎉