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