Hi Mona, how are you? I hope you are doing just fine!
1) Would: it is the past tense of 'will'. It is used to express desire or intent.
E.g.: ''If I won the lottery, I would buy a big house.''
E.g.: ''She said she would meet us there!''
E.g.: ''I told you he would betray us!''
2) Can / Could: ''Can'' is used to indicate possibility, and express physical or mental ability; whereas ''Could'' is the past tense of 'can', used to indicate ability in the past or to express politeness.
E.g.: ''I wonder if my lost dog can still be alive out there.''
E.g.: ''Can you remember the war?''
E.g.: ''I could run as fast as you just did!''
E.g.: ''Could you open the door, please?''
''Could'' can also be used to talk about possibility in the present or future. You use ''could'' to say that there is a possibility that something is or will be true.
E.g.: ''Don't eat it. It could be poisoned.''
E.g.: ''He was jailed in February, and could be released next year.''
IMPORTANT: ''Could'' is also used to talk about ability in the present, but it has a special meaning. If you say that someone ''could'' do something, you mean that they have the ability to do it, but they don't in fact do it.
E.g.: ''We could do much more in this country to educate people.''
Hope that helps!!!