Will,

What you've linked to is part of the technical standard, it's certainly not necessary to understand that in order to use abc. This is far more understandable:

Steve Mansfield's ABC tutorial

Like everything, it takes a bit of effort to learn, just as notation does, and some understanding of music notation which is what it represents.

I'm sure many people use it as I do, as a keyboard-entry method of creating notation which I can then play back, print or save as a pdf using either a software package such as ABCExplorer or a web converter.   I find this quicker and simpler than drag-and-drop which other software packages use (some also offer keyboard entry, but I prefer ABC as it is the de facto standard for sharing folk tunes). Being able to play it back helps me check that I have written it correctly and so helps improve my understanding of notation.

ABC is most efficient when writing out single-line unharmonised melodies, so it is ideal for folk tunes (which is what it was designed for). It can handle more complex music but rapidly becomes unwieldy, and there are better alternatives if that is the sort of music you want to write.