Bokmål is the most used writing form in Norway. Norway used to be under Denmark and when we became a free country we wanted to create our own writing language since we had been writing danish for so many years. Bokmål is the writing form that was based on danish and is the more "posh" writing form. Nynorsk is the writing form based on the many dialects in Norway. Ivas Aasen who "created" nynorsk travelen around Norway and gathered dialect worlds and made the writing form. I can't really tell you how you can know the difference when you see it, I guess you just have to know^^ Hope I answered your question okay.