Hi Karim, The first set (don't, didn't, doesn't) are example of the auxiliary verb 'do' in various forms. 'Don't' and 'doesn't' are the present simple negative forms - doesn't for 3rd person, don't for every other conjugation. I don't like ice cream. (1st person) You don't study science. (2nd person) She doesn't play tennis. (3rd person) 'Didn't' is the same auxiliary but for the past simple, every conjugation. I didn't go to school yesterday. (1st person) You didn't call me. (2nd person) He didn't see the movie. (3rd person) 'Won't' is the negative auxiliary 'will' - this has a few uses, but most often it is used to make a spontaneous decision about the future, or a prediction about the future. No thank you, I won't need any help with this. (spontaneous decision) It won't rain tomorrow. (prediction) 'Would', and it's negative 'Wouldn't', is modal verb, expressing volition (the desire to do something) in the affirmative form 'would', and lack of volition in the negative form 'wouldn't'. It is often found in suggestions and conditionals. If he had asked, I would have helped him. (3rd conditional) If I were you, I wouldn't buy that car. (2nd conditional) 'Could' and 'Couldn't' are a bit tricky. Sometimes 'could' is a modal verb similar to 'would', but expressing ability/possibility (and lack of when using 'couldn't') If they won the match, they could go to the finals! (2nd conditional) If he hadn't helped her, she couldn't have done it. (3rd conditional) 'Could' is also the past form of 'can', a verb in the past tense expressing ability/possibility in the past. We could drive around town. (past simple affirmative) I couldn't read until I was 4. (past simple negative) ****Would and could are also used in polite exchanges: Would you like a cup of tea? Could you pass the butter please?**** 'want' is a regular verb expressing desire/volition. I want to go to Jamaica. (1st person present simple) Hope that helps a bit!