Well I put the first one down... with the roots and about 1/2 inch of onion attached. We'll see.
Anytime you buy an onion in the store to use, you can grow your own.
The pointy top part of the onion, you might as well cut up and eat.
But if you slice off the rooty, bottom part, put it in the ground, water it good, and leave it alone.
Onions are very hardy, it will grow at least one new onion, possibly more.
Same is true of celery.