problems w/ slackpkg
 

I'm assuming slackpkg is used similarly to apt-get. For instance, you type
It's not working for some common packages, however (i.e. hping). In fact, it won't work for ANY packages unless they're already installed and I type
This will take me to a window that looks like the pkgtool command w/ the nmap package in a ncurses window.

Any advice?

slackpkg is intended only for packages included in Slackware. But hping is a third party package, so slackpkg can't install it. If you want to install it do:

Why is there a mirrors file? I was beginning to think that's a file similar to sources.list like in Debian.

Because slackpkg has the capacity of updating from the chosen mirror the list of packages included in Slackware (following the Changelog) so that you can use functions like "slackpkg upgrade packagename" or "slackpkg upgrade-all". Then slackpkg will download the involved package(s) and upgrade it for you.

It can similarly download and install a package you would have not installed or removed with "slackpkg install packagename".

"man slackpkg" will tell you more.

EDIT IIRC slackpkg has abilities similar to apt-get's, but two important ones:
(a) It can only deal with the official Slackware repository or one of its mirrors.
(b) It doesn't deal with dependencies. This is not needed with Slackware as the dependencies are always met, provided you made a full installation.

What exactly is a Changelog?