Is there a difference between "Buen" and "Bueno"?

Well, we need to take into consideration two aspects of these two words. The first one is the fact that both are the same in meaning. This means they are both used to describe singular masculine nouns. The second one is where you'll put them in a sentence, and this is the difference between these two words. "Buen" goes before the noun and "Bueno" after. So, the following two examples are the same in meaning: El es un buen hermano. He is a good brother. El es un hermano bueno. He is a good brother.