"Would" and "could" are usually used with a condition.
e.g. I would cut the grass, but it is raining.
I could cut the grass if my mower was sharp.
"Will" is what you intend to do no matter what.
I will cut the grass (whether it is raining or not).
"Can" is what you are able to do no matter what.
I can cut the grass(even with a rusty mower).
- For Teachers