How to transfer mail from Yahoo to Gmail?

Answer 1

...from a Gmail help article:

Moving mail from another account to Gmail

There are three ways to move your mail from another account to Gmail: forwarding mail, importing mail, and fetching mail. Regardless of which way you use, we suggest creating filters and labels in Gmail to help organize this mail. Select an option below to learn more about moving mail, and to see which method will work best for you.

Transfer existing mail and/or contacts to Gmail:

If you're switching to Gmail from another email provider, importing contacts and messages from your old email account can help you make the transition without having to do a bunch of housekeeping. You can also have new mail sent to your old email address automatically imported to your Gmail account for the next 30 days. Please note that this doesn't establish a permanent connection between the accounts. If you want to connect two accounts permanently, you should use Mail Fetcher.

Transfer existing mail to Gmail, and check for new messages regularly (Fetching):

Gmail's Mail Fetcher can download messages from up to five other email accounts on a regular basis, centralizing all your email in Gmail. If your other webmail account offers POP3 access, you can configure Mail Fetcher in Gmail and automatically download all your other mail to Gmail. In a short amount of time, this will download all of your existing messages to Gmail, and will regularly check your other account for new mail. You'll need to contact your other webmail provider to determine whether or not they support POP3 access, and for instructions on enabling it.

Transfer new mail to Gmail (Forwarding):

If your other webmail provider supports auto-forwarding, you can set your Gmail address as the forwarding target. This will only forward mail that arrives from now on. You'll need to contact your other webmail provider to determine whether or not they support auto-forwarding, and for instructions on enabling it.