Slackware book and `slackpkg`

Hi all,

As a Slackware newbie, the question might be a bit wrong, but I came to know about `slackpkg` by mistake (in some other forum thread).
The Slackware book (http://www.slackbook.org/html/book.html) has no mention of this. Can you please point me to where/how a Slackware newbie should have known about `slackpkg`?

Thanks.