What does by "floss the teeth you want to keep"? aren't we suppose to floss every one of them everyday? ty

Exactly: So that is exactly what you need to do. It it just a phrase to help you remember to floss.

Yes, you are correct: Floss each and every one of them. The phrase is a play on words; by saying "brush and floss the teeth you want to keep", it is implied that since you would want to keep all of them, you should take care of all of them.

It is that simple...: Yes, floss only teeth you want to keep, and forget the rest! You see, next to brushing, flossing is the most important thing that you can do to ensure good oral health.