It's a casual and informal way to refer to a man, often used among friends or in relaxed settings.
Examples:
* "Hey, fella, how's it going?"
* "That fella over there is my brother."
Note: While "fella" is typically used for men, it can sometimes be used more generally for anyone, regardless of gender, especially in informal contexts. However, it's generally more common and appropriate to use "fella" for men.