THIS IS A TRULY GREAT BOOK THAT STANDS THE TEST OF TIME!!!
The newest 3rd edition, purple cover sells for $70 or so. But you can find the 2nd ed, red cover, in used book stores. or on the web.
Here is a book that has the answer.
"UNIX System Administration Handbook" By NEMETH, SNYDER, SEEBASS, HEIN
FROM THE BOOK page 708-709 by column:
1) service name ( ftp, telnet, etc... )
2) Determines the type of socket, either stream, dgram, or raw. In general, stream is used with TCP, dgram with UDP, and raw is rarely if ever seen.
3) communication protocol
4) user name underwhich the daemon should run. (You could call it BOB if you wanted)
5) The User name it should run as.
6) The remaining fields give the command line and its options.
Remember this entry also needs a companion entry in the /etc/services file for it to run.