If it's your first time using Mango through your library, you'll need to make a Mango profile. This is different than your library profile, which you may log in to using your barcode and pin.
To get started, click on the Mango Languages link on your library's website. On the Mango log in page, click where it says "Don't have a profile? Create one" at the bottom of the screen. Then enter in your information and click the "Sign Up" button.
Then the next time you access Mango through the library's website you can log in with your email address and the password you created.