Shall vs Should, Can vs Could and Will vs Would

[che5ter]

I'm confused with this words and how to use them.

"Can" anybody explain this? Any help "would" be appreciated.

[bogdanno]

i use shall as a polite form of future, especially in questions
shall i go then?
you should means you must,
you should make your homework

can is used in many forms
informal
can you do it?
or ability
he can swim

would is used as a possibility that didnt happen:
he would have done that if he had know
or
as a possibility in general
i would go out with him to theater tomorrow( if he asks me)

i don't use "could" much
i guess its a polite form of "can"
could you do this service for me?
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The reader is encouraged to correct my English mistakes.