What is the difference between dude and guy and fellow and fella and buddy ?Feel free to just provide example sentences.

Guy- is an older boy, like over age 12 or so. Used similar to boy.
Fellow-is a more formal way to say guy. We don’t normally use this. If I’m not mistaken it’s a southern word that was used 100’s of years ago. Occasionally you might hear it, but it’s rare.
Fella-is the same as fellow, but this is spelled more like a southern person might pronounce it. It’s just written that way sometimes cause that’s how it sounds when some people say it. Exactly the same. Just written that way for fun, like slang.
Buddy- means friend. Sounds odd to me. It can be a pet name too. A different, more weird or cutesy way to say friend.
Dude- is a slangy, cool way to say guy. You use it a little bit differently though.