First let me correct your question: we say "...the difference between" and not "among". Should: is used in a certain number of situations, for instance: - to give advice or to give an opinion: You look tired you should go to bed. - When something is not right or what we expect: I wonder where Liz is. She should be here by now. Would: Is also used in different contexts for example: - when we imagine a situaion or action: It would be nice to have a holiday but we can't afford it. - we use would have (done) when we imagine situations or actions in the past: They helped me a lot. I don't know what I would have done without their help. Can: Is used to say that something is possible or that somebody has the ability to do something ( can + infinitive): We can see the lake from our bedroom window. Could: Sometimes could is the pasr of can: When we wnet to the house, we could smell burning. - We also use could to say that somebody had the general ability or permission to do something: My brother could speak five languages. Must: is used to say that we feel sure something is true: You have been travelling all day. You must be tired. Might: is used to say that something is a possibility : It might be true. You will find further explanations in "English Grammar in Use", Raymond MUrphy, Cambridge University Press. NB: I have used this book in my answer.