How do I forward mail from another email address ...

You might try using AOL Easy Transfer.  This will allow you to forward emails, among some other options available, from an existing email account to an AOL account.  Emails will be forwarded for 30 days.  While it is not possible to setup automatic and permenant forwarding, you can use Easy Transfer as often as you like.  It is free.

To access Easy Transfer, click on Settings in the upper right. Then select Accounts from the menu on the left hand side.

Under the Transfer Accounts section, you will see a link to AOL Easy Transfer.  Try it out.