okay ,could has 2 meanings (1) we use could to ask for stuff in a polite way ,for example ;could i have a class of water. we also use could for simple past for example; I could read when I was 3 yeas old. we use would for offer and request .for example ,(1) would you like to have dinner with me.that is called an offer. example(2) I would like a class of water. that is called a request. Should is used to give advice for example ,you should brush your teeth before you go to bed.

COULD CORE-MEANING: a modal auxiliary verb used as the past tense of "can" My mother did the best she could for my brother and me. She could perform on the trapeze. His feet were so swollen that he could hardly walk. We were so tired we couldn't stay awake. WOULD CORE-MEANING: used to express the sense of "will" in reported speech or when referring to an event that has not happened yet Susan didn't think she would pass. It would be wrong to suggest otherwise. SHOULD CORE-MEANING: modal verb indicating that something is the right thing for somebody to do You should get more exercise. I should have told her I was leaving. The report recommended that children should be tested regularly.

"What is the difference between could, would, and should?" "When and how do you use all these words?"