Forwarding is as easy as it sounds.
First, click Options in the upper-right corner of your Mail page and select More Options.
From the list on the left, click POP & Forwarding.
Click inside the circle next to "Forward your Yahoo Mail". Then enter the email address in the blank and click "Save Changes."
Your mail now gets forwarded to that email address.
Note: You can’t simultaneously Forward and POP your mail.