In order to do transfers and some other operations, you need to get the security clearance. This is done by receiving a code on the cell phone.
On the left side of your Banco do Brasil page, there is a toolbar, near the bottom find: Segurança → Solicitar código de liberação. This should send a token to your cell phone.
There are substantial delays between you making this request and Banco do Brasil actually sending you SMS
Sometimes after you enter token, it may take up to 4 hours of delay before you are actually granted the clearance. The site will advise about that delay (but not about the delay in sending the SMS)
Your session may expire before you get your SMS. In that case, re-login and find Segurança → Informar código de liberação.