I can't believe that noöne's replied to you yet on this matter. I don't know if you still need help with this, but here's something for those who do:
In Spanish the letters b and v are pronounced as /b/ at the beginning of words and after consonants. After/between vowels the two are pronounced as what's known as a "voiced bilabial fricative", which is represented as /β/. It's similar to the English sound /v/ but it's slightly different. The English /v/ is pronounced with the bottom lip and top teeth, whereas /β/ is pronounced using both lips. To my knowledge no natural language distinguishes the two, but if achieving a native-like pronunciation is important to you (it definitely SHOULD be, in my opinion) then you should learn the difference.
I hope this helped someone out!