I will try to show you the use of these modal auxiliaries as they can be quite complex but I will try to give a quick answer. Notice in my sentence above "I will try." The "will" expresses willingness, sometimes called volition. Sometimes it just expresses future time, but in current English "be going to" and simple present can also do this. 'Would' is often called the past of will, but it also expresses other thoughts. It can mean willingness to perform a hypothetical action, such as, "I would help you if you needed help." In this sentence, you do not need help, but I would help if you did. 'Would' can also be used to express habit in the past, as in "When I was a child, I would sleep with my teddy bear." 'Can' expresses ability. 'Could' is often called the past of can, and is used the way 'would' is used in a hypothetical situation, where the speaker wants to express ability instead of willingness. 'Could' sometimes also is used to make suggestions. Example: We could go to the beach, or we could go to the park. 'Shall' is not much used as much in American English as British English. Its use is mostly confined to utterances such as, " Let's go, shall we?" "Shall I pick you up at 7pm?" 'Should' expresses advisability--that something is a good idea. If I think you are sick, I say, "You should go to the doctor." Less often we use 'should' to make a prediction about something we think will happen. Example: The train should come in five minutes.

BASIC RULE:- Will, Can,Shall are verbs used to describe the sentence or speech in Present tense. Would - is past for "Will" and used for Past tense. Could - is past for "Can" and used for Past tense. Should - is past for "Shall" and used for Past tense. --------------------------------------… Will- a wish with certainity or surity. WILL = I will do the the work for you. (It means, at the moment or now ,certainly I will do the work for you) WOULD (past of 'will) = If I were at home with you, I would do the work for you. (it means,if I were present at the time you were doing the work,I would have done it for you.) --------------------------------------… Can - is able or is capable. CAN= I can do the work for you but it depends on my mood. (it means, I am capable to do the work as required,but I may or may not do the work. If I feel like doing the work,I will do the work and if I feel like not doing the work, I will not do it.) COULD (past of 'Can') = I could do the work for you,but I wanted to sleep. (it means, I am capable of doing that work,but I didn't do because I wanted to sleep) --------------------------------------… Shall - may or may not (a wish of uncertainity-may be or may be not) SHALL = If I get extra time,I shall do the work for you. ( it means, I may do the work for you,if I have sometime left after I complete my work,else if I have no time, I may not do the work.) SHOULD (past of 'shall') = I had an extra time,I should have done the work for you. (it means, I could have done the work because I had some extra time on hand,but even then I didn't do the work for you.