Reorder level - how to use

I want to be able to set up a level at work I want to reorder an item.

In an item page, under the inventory tab, I found a section called auto reorder.

I presume I put in the minimum quantity I want to keep in stock?

It allows to to place a quantity. Can I leave it blank an ddecid elater? Can it be th edifference betwene reorder level and current quantity?

=There is a note saying “Will also apply for variants unless overrridden”

Will this apply to all variant using the same template? How can I make it apply to 1 item only?

Thanks for your assistance.