I. 1. Always use could and would with the words “wish” and “hope”.
Examples: 1. I wish I could go but I can't. 2. Their wish was that the date of the party would be changed. 3. We wish we could come but we can't. 4. We hope that the costumer would reconsider.
2. Use could and would as a polite way of asking.
Examples: 1. Could you call him for me? 2. Would you vote for me? 3. Could you do me a big favor?
II. A. Use can to indicate ability.
Examples: 1. She is resigning because she cannot cope with the responsibility. 2. She cannot tell us the source of the rumor right now.
B. Use could to: (a) indicate the past of can. (b) some possibility with strong undertones of certainty. (c) contingent possibility with an "if" or "when" phrase.
Examples: 1. He could not take me home yesterday. (past tense of "can") 2. The road could be safe, but I'd rather not risk it. (possibility with strong undertones of certainty) 3. If I had more money, I could take that trip. (contingent possibility) 4. When the strike is settled, we could reopen negotiations with your company. 5. We would like to know when we could see you. 6. Our analysis would not be complete without your contribution.
III. Use will to: (a) indicate action in the immediate future (b) express willingness (c) make a prediction
Examples: 1. The race will start soon. (future action) 2. She will help us with this project. (willingness) 3. I am sure he will be here soon. (prediction)
IV. Use would to: (a) indicate uncertainty in the future (b) probability (c) habitual past action
Examples: 1. Would you agree to have another meeting? (uncertainty in the future) 2. The candidate would present his platform if the group were willing to to listen. (probability) 3. Every evening last week, on my vacation, I would take a walk by the sea. (habitual action)
These are just a few of the examples that you can create using these CAN/COULD and WILL/WOULD.