This tutorial provides step by step instruction for setting up Yahoo Mail on Mac OS X Lion. Mac users can configure Yahoo Mail using the Add Accounts menu option available as part of File menu.
Click the File menu and select Account from list of displayed menus.
In the Add Account screen, enter the Full Name, Email Address and Password of your Yahoo mail then click the Continue button.
The Account Summary screen would display account information as shown below.
If you want to configure Contacts, Calendars and Chat then mark the respective checkboxes and click the Create button. Now the Yahoo Mail box would be available under Mailboxes.