Language At The Table

Help!

I’m trying a new interactive website to help with my Dutch lessons, and I’m starting from scratch to try to get a review of some basics as well as learn some basics I haven’t covered before. Today I’m working on prepositions, as well as the concept of stuff/people sitting at the table or being on the table (among other examples). I’m getting nit-picky and confused, though.

Question #1:
De bloemen staan op de tafel.

Het eten staat op tafel.

Why is de used in the first example (op de tafel), but not in the second (op tafel)? Is there a rule that explains this?

Question #2:
When do items stand on the table versus sit on the table (or any other surface)? E.g.,
De koffie staat op (de) tafel.
vs
De koffie zit op de tafel.

Are both correct? Is one used more than the other? Do I use “de” at all?

I’m trying to look up the answer in some of my other sources, but sometimes it does help to have a person do some explaining, as well. Any explanation will be greatly appreciated.