This is a great way of getting the latest research from your 
favourite journals to your inbox. Usually you will need to create a personal account on the journal website and validate this by following a link sent to your email inbox. Even if this is optional, creating a personal account is always advisable so that you can delete or edit your alerts.
How to set up new issue alerts
This depends on the platform. When you are in a platform like Science Direct, you will see an option to Sign in/Register. Once you have registered with that platform, you can choose to get email alerts when a new journal issue comes out.
Overwhelmed by email alerts?
You can avoid your inbox being overwhelmed by alerts by setting up rules in your email account to divert them into folders.
For information on how to do this, see Manage email messages by using rules.