"Vow" is a very serious or solemn promise. "Pledge" can mean the same as a vow, or, it can also mean something that you give someone as proof that you will complete your contract or agreement with them. "Oath" can also mean the same thing as vow, but sometimes includes the aspect of your promise being witnessed by a higher power or authority. "Vote" is different and is a gesture of approval for someone or something.

"Could you tell me...?" is the question. Honestly, use a dictionary. A short explanation is, vow and pledge are promises. A vote shows your preference. An oath is an affirmation.