Short answer
HubSpot's KB: Send internal email notification emails specific users, teams or owners, works in all workflow types, and supports tokens from the workflow's object. Send internal marketing email (Marketing Hub Professional and Enterprise) sends an automated email to specified addresses or a property holding an email address. There's also Send in-app notification.
1. The actions
Searching the action picker in my demo portal.

2. Not for customers
To email enrolled contacts, use the Send email action with a marketing email.