Do you have a BB data plan? Once you have that, I suggest a read of the FAQ. Here is one article that might help: How to add / delete email addresses - BlackBerryFAQ
I do not recommend using the carrier supplied email address however. First, if you use it a lot and it gets "harvested" then you are open for more SPAM than you care to get as it is totally unfiltered.
Second, the only way to read email to that account is on the BB itself. No web mail option, so when there is a data outage, no email.
And third, you cannot take that address with you when and if you change carriers.