Please help me use Mail app?

Hi there, please help me gain access to Mail app?

I used a gmail address for my Apple ID since 2000 for my app store/itunes purchases. I recently updated the ID to an outlook address.

In both cases, whenever I click on the Mail app, it tells me that I need an icloud email address.

I currently have an iCloud address; does this mean I connect this email?

Most of the information available on the internet -- whether from Apple or otherwise -- is very unclear.

Cheers,

Michael