Can : Able to.
Will: Expresses a request for action.
shall: Expressing a demand or assertion; first person future.
When i ask "Can i do _this_?" i would be asking "Is it possible for _this_ to be done the way i am describing?"
the possible answers are "yes, u can do it and this is the way to do it." OR "No, you cant do it, because its not possible OR because you know it is broken(technically) and cant be fixed"
The answer should in all cases, NOT be: "i will do it for you".
When i ask "Will you do this?" i am trying to bargain, because i know i have some restriction in doing it, i know i can do it, but its a request and a confirmation if you want to do it. the possible answers are "no, i cant do it because its impossible for me do it now" OR "yes, i can and i will do it".
when i say i cant do something: it means its impossible for me to do something.
when i say i dont want to do something: it means it goes against my interests.
XKCD Comic
