Buddy is a term that means friend, usually just boys. Friend is a much more common term, and works better in most situations. To me, buddy sounds a bit childish, it is used more around children.
On the other hand, buddy is not always used to mean friend, such as "Hey, watch it, buddy!". This phrase can be used when another male person is being careless, and reckless, and putting you, someone else, or something in danger..