Bokmål & Nynorsk

Hi everyone could someone explain me the difference between Bokmål & Nynorsk? Are they two different languages both spoken in Norway?
Wikipedia.org says that they are two different form of Norwegian language or better two different writing system of Norwegian...but I still do not understand: they are different only in the written form or, also, in the spoken form (phonetics etc)...could we consider them as dialects or as two different languages? could a Bokmal speaker understand a Nyorsk and viceversa? Please someone explain me! Thank you!

Opss....I forgot a question: out of Bokmal and Nyorsk is there a standard Norwegian language used in acts, school, documents, comunication (TV, Radio, Newspaper etc)?? Thank you again!

Well, Bokmal is used mainly in southern Norway.
Nynorsk is used mainly in western and northern Norway.
But you can find many dialects in southern Norway that are between Bokmal and Nynorsk, or even, closer to Nynorsk. Nynorsk is closer to dialects of Norwegean, while Bokmal is Danish-influenced Norwegean.
For most nice jobs, many times, knowing of both Bokmal and Nynorsk is required.

My understanding of the situation comes mostly from Wikipedia, but I'll try to explain it. Bokmål is a Norwegianized form of Danish that was developed in the early 20th century from Dano-Norwegian, the language spoken by the upper classes in Denmark-Norway. Nynorsk, on the other hand, is the standard language based on the Norwegian dialects and intended to be a more national alternative to Bokmål. Both are currently official and taught at school. However, the vast majority of Norwegians use Bokmål for writing, even though their speech is closer to Nynorsk.

When written, Bokmal is very much like Danish. However, it is very different from Danish in pronunciation.