Question

when we use would,could and should?

Answer 1

1. Would is used in Indirect speech for will. It indicates ability of something/someone to do a work in future. Ability of Future is would.
2. Could is used in Indirect speech for can. It indicates ability to do now. Ability at present is could.
3. Should is compulsion. Necessity. It is not used in indirect speech for shall as they both have completely different meaning.
For Eg.,
1. He would drive a car.
He will have the ability to drive a car in future.
2. He could drive a car.
He has the ability to drive a car at present.
3. He should drive a car.
He has to drive a car at present.
Hope you understand.

Answer 2

Could is choice
Should is compulsory