Contact your carrier and request BlackBerry Internet Service be enabled on your account. The BIS service is usually packaged with a data plan of several Mb.
Once the plan is active, you will be able to use the Email Setup app on the BlackBerry.
Your carrier set up your account in those sites. You have to create your account in the site and have activated your BIS data plan.
As a second hand blackberry I recommend you to CALL first for them to check your IMEI or PIN and tell you if it already registered or if is marked as stolen. And then contract the data plan.