Do I need Gmail, Outlook, Apple, etc. to use HEY?

No. HEY is an email provider, it’s not an app you use to check your existing Gmail, Outlook, Yahoo, etc. HEY is a replacement for those services. HEY is all you need to send, receive, and organize email. You can forward your current email to HEY, but when you sign up for HEY, you’ll get a brand new @hey.com email address.