Writing R library

You should start creating a separate directory for your package
(e.g. foo).  As a minimum you need three things:

1) your R functions (as .R files in directory foo/R)

2) documentation of your functions in .Rd format (look "writing R
   extensions" and function prompt(), they must reside in foo/man directory)

3) The DESCRIPTION file (in the foo directory).  Everything else is
   made by R.

Now run "R CMD build foo" in the directory above (where the subdir foo
is lying).