Wow Thank you Chris and Leslie, I do understand it now. :)

"Barking dogs seldom bite" is literal and "all bark no bite" is a colloquial expression. Barking dogs seldom bite means that if a dog wants to bite you, it won't waste time barking; it will just bite you. A barking dog might be a social dog, or a scared dog, but not necessarily a mean (biting) dog. All bark no bite is an expression that means a person threatens, but does not make good on a threat (e.g., a parent might say to a kid, "if you stay out past midnight, I'll hit you with a belt," then when the kid gets home after midnight the parent doesn't hit them with a belt).

Barking dog seldom bite means they rarely bite but i can happen, and the other saying all bark and no bite means they don't bite at all. Of course these aren't used for dogs but for people so the first one could be used like this 1. Barking dogs seldom bite but when they do watch out 2. Ashely is all bark and no bite so don't worry about her. In my opinion the second is better and used more often than the first. both convey similar meanings about people and their personalities. hoped it helped!