Cannot get to the screen where I enter my email address and password.

Cannot get to the screen where I enter my email address and password to see my emails.

The att/yahoo webmail is accessed by going to att's home page, start.att.net, and clicking the mail icon in the upper right.

I was led by support person into using my an email address to access billing, directv etc. Now when I want my email I end up in billing etc. What is the URL to take me to an email login screen??

Not sure now what you want.  Email or account management.   Accounts are managed through your myAT&T which you can also get to through start.att.net (link in left hand column) or going directly to what that link points to, i.e.., https://www.att.com/my/#/login.