When I email something or download a program, or do anything else over a network, where in the segment is the actual content? If I am emailing a 20KB word document, and the maximum data field size in a segment is 1500 bytes, does that mean it takes about 14 segments to mail my document wherever it is going?

I get, I think, the OSI model and I have a decent grasp of the IP protocol. I think I understand the concept of header wrapping of each successive layer in the protocol stack. What I can't get a definitive answer to is where does the actual content go in a TCP segment? Is that the datagram?

Maybe the fact I am asking proves I have no clue...

Many thanks.