Question.  Why is there no help in the Mathematica Documentation Center about a function you (Murray Eisenberg) defined?

Answer.  The Documentation Center ordinarily includes help only about functions and other objects that are built into Mathematica or are part of standard add-in packages that are distributed with Mathematica.

That´s why, in the notebooks where I define such functions, I ordinarily include usage message definitions that you may access with “?” in the usual way.  For example, if I define a function doit for you to use, you could obtain help about it by:

?doit

You can create usage messages for your own functions, too.  To create a usage message for your own  function myFunc, simply evaluate an expression like:

compositeQ::usage =
  "compositeQ[num] returns True if num is a\n composite integer, and False otherwise."