Won't is the contraction for will not Which is used for future tense. Would is the past form of will , and woudont is the negative form of wound , and used in situations where something may have happened but did not happen in real. Wouldn't is a more polite way of conveying something when compared to won't.

won't means will not. Wouldn't means would not .

Won't" is the short form of "will not". 'Wouldn't" is the short form of "would not" and would is the past form of will. Won't and wouldn't are very common and informal in use, whereas will not and would not are usually formal. Won't = will not is used when you are certain/have planned for something that is not going to take place in the future, for example he won't go to London, I won't lend you any more money, the door won't open, etc. wouldn't = would not is used when we talk in the past about something in the negative about future, for example, he said he wouldn't lend me any money, I promised I wouldn't smoke any more, I assured my mother I wouldn't waste my time, etc.

Won’t is will not. I won’t go to work tomorrow because it is a holiday I would say won’t, when I want to express something that I am not going to do in the future. I wouldn’t say that … I would never get a tattoo because I’m afraid of needles. Would still gives you a window to change your mind, but I think they are pretty close.