I'd like to partecipate, too.
I read most of "Part 1" and it seems quite understandable and easy to follow for the general public. I'm actually familiar with those concepts, so even I'm trying to be objective you may still consider this comment a little biased.
I noticed that there are a lot of pictures about asymmetric cryptography, while the explaination of symmetric cryptography (3.1) has not a related picture in-page. Something related to bad guys intercepting the key may be an idea.
Just to be picky, in 4.6 there are some (misplaced?) dots.
Keys are the basic component of asymmetric. cryptography, also know as public key cryptography.
To be used they must be stored in key rings., which GnuPG creates automatically.
Hope this helps.