Will indicates a ‘willingness’ to do something in the future. The negative form of will – will not (won’t) indicates an ‘unwillingness’ (refusal, reluctance) to do something.
Example:
- I will give you another opportunity.
- I will play tomorrow.
- They will arrive at 10 AM.
- She won’t come today.
Would indicates general or repeated willingness in the past. It also indicates preference in the present.
Example:
- If you did not leave, I would still be taking care of you.
- Whenever I had to go there, they would throw a party.
- We thought that people would buy this book.
- If I were you, I would not do it.
- I would like to make a toast.
Used to sometimes replaces would but sometimes it would be grammatically incorrect if we use used to in place of would.
Example:
- When I was in school, I used to make sketches.
- He often used to cry at night without reason.
- I used to take a break at this time of the year.