"Give someone a hand" I know thing from the Addams Family was pretty useful but that might be a one of a kind, so unless the person needs a paper weight or doorstop I don't see how just a hand is very helpful.
It might have been used in The Addams Family but that's not its origin. It's an old and very common phrase, meaning to help someone with some task or other.
It might be maritime originally - the crew of ships having been known as "the hands" for centuries.