Fella is basically an antiquated slang for "fellow". I would never use the term. I've seen it used in old television shows. They would address a stranger in a harsh tone. "Hey fella, move along, you can't drink alcohol while sitting on that bench". I think Lucy from the television show "I love Lucy" used that word a lot.

Hi Andris, The word "fella" is used in casual and informal speech. It means "fellow" or someone's boyfriend. In turn, fellow means someone else pursuing the same activity or interest as you. Example: Dear fellow colleagues, please take a seat. A friend is a person whom you socialise with and probably share similar interests and support each other. Hope this helps. Cheers, Lance

Fella is to refer to someone usually a male stranger in a friendly way. Friend is just friend.