Their Linux CDs proved essential in a time where bandwidth was scarce and expensive with home users on dialup and only universities having a few megabits of bandwidth.
Not only that - the distribution my dad brought home included a _book_ (remember those?) which was actually a bunch of open source books collected in one! Tons of information on Unix stuff, shells, commands etc. I learnt so much from those books. I have no idea how someone would start in this day and age... (this was so important to tell for me that I finally stopped lurking and made an account _just_ for this comment!)
You start by having someone tell you about man -k. That, plus playing (typos → error messages → more words to look up) is probably sufficient.