Hi there! They are confusing words in some contexts. But basically, you can always remember: - Can is the most common word, to describe your abilities, or you use can to ask for a permission, a request, too. Ex: I can understand. / Can you swim? / Can I borrow your car? - Could is the past tense of can. Ex: I could play football when I was a child. Also, could is a more formal way to ask for a help, a permission (like can, but more formal!). Ex: Could you please help me to translate this? - May is commonly used to talk about prediction, something is possible. Ex: It may rain. / They may win the battle. - Might is the past tense of may, and quite similar to may in usage. Usually, you should use might to make a polite suggestion. Ex: You might try calling him tomorrow. / Might I use your phone? => can/could/may/might can be used to ask for something. To avoid confusion, you can simply use can or could. - Must is used to say something that is very important, and you are requested, are forced to do. Ex: You must wear uniform in this company. / You must pay the tuition fee to learn at this school.

hi,你是要学习中文么

this is a huge subject that is difficult to explain in a short post, they are auxiliary verbs, you might want to look them up here is a link that gives a basic idea for each http://www.talkenglish.com/Grammar/auxiliary-verbs-can-could-may-might-must.aspx

Creo que te será mas fácil saber cuando usarlo, si los asocias con las siguientes equivalencias al español: I can do it - yo puedo hacerlo. I could do it - yo podría hacerlo. I might do it - yo pudiera hacerlo. I must do it - yo debo hacerlo. ¡Ojalá te ayuden!