problem with dates

This is a rather generic question about "date" and "time". I seem to
be beating my head on the wall. I was trying to use a set up a table
with a 'date' and 'time' field. I wanted to keep the two separate.

Can someone explain if there is a difference between a time field
and a timestamp. I don't mean the visual date and time as a single
element. I mean in concept. I have been pouring through the docs
and it appears from my reading that a 'date' field is supposed to act
like the date portion of a timestamp. But it doesn't and I just don't
understand why.

if there is some document somewhere that explains this just point
me to it.

Thanks again.

Ted