This one was written for my brother-in-law who often challenges my perception of "ease of use". Apparently Google's well written instructions are not as easy as I think they are.
You can get mail from your other non-Google accounts. You'll be able to read your email all in one place, and take advantage of all of Gmail's great features. To setup Gmail with other account do the following:
Login to your Gmail account and click the “Setting” link in the upper right hand corner.
You will be taken to the “Settings” page. Click the “Accounts” link.
On the Accounts page look for this section click the “Add another mail account” link.
Enter your non-Google email address in the “Email address:” text box and click “Next Step”.
Enter your password and click the “Label incoming messages:” checkbox and click “Add Account”.
Similar instructions are available on Gmail Help Center.
Once your account has been added successfully, you'll have the option of setting it as a custom From address. This allows you to compose messages in Gmail, but have them appear to be sent from your other email account. Google will check your other account on a regular basis, and new mail will appear automatically in your account.