So what is Debian at all?

Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run.
Debian GNU/Linux provides more than a pure OS: it comes with more than 3950 packages, precompiled software bundled up in a nice format for easy installation on your machine.
It's a bit like a tower. At the base is the kernel. On top of that are all the basic tools. Next is all the software that you run on the computer. At the top of the tower is Debian -- carefully organizing and fitting everything so it all works together.
Although Debian believes in Free Software, there are cases where people want or need to put commercial software on their machine. Whenever possible Debian will support this. There are even a growing number of packages whose sole job is to install commercial software into a Debian system.