To set up a new mail account on your Mac, go to Mail → Add account ...
Then you'll see a new window. Click on "Another email account ...".

A new window will open in which you can write the name you want, the email address and your password for that account, and then click on login.

Probably after the log in you'll see an error message, telling you that it was not possible to verify the name or the password inside the following window, where you will need to write the email and password again, an more options. The type of account should be IMAP and in incoming and outgoing mail server you have to enter "" (if we aren't your email providers you should ask your provider for this information). Once all the info is typed in, press on Log in again.

You'll probably see a message that says "Mail cannot verify identity of server....." Click on "Show certificate"

It will take you to a window where you have to click on "Trust always in ..... "  and then continue.
Then you'll see a windows asking for the password of your COMPUTER (in case the computer has.) Type in your password and you'll go back to the previous screen.

Click on the "Show certificate" button again.

And then follow the same steps, select "Trust always in ..." and click on Accept. You'll be asked again for you computer password, introduce it and accept.

And finally you'll see a list of apps that can be used with your email account. select the ones you like and press on Accept.

Your email accounts is now configured on your Mac!