When I signed-up first into Zoho (general), I used my gmail.

Then I subscribed into zoho mail using my gmail again.

I tried to set up my zoho mail under my domain name, then in order to use my domain name in my zoho email, I have created a new email address with my domain. 

I am confused when I need to use which one? I think with other zoho apps there will arise same question for me.

Please explain me.

BR

Zorge