Way back in the day, the help documentation shipped with MSDOS really helped me out. IIRC it had a colored text-graphical interface that let you look at all the commands and what they could do.

Really helped out a young kid figure out how to write autoexec.bat/config.sys files so that his games could run. Being able to write menus so I could customize my setup for each game was so amazing.

With the advent of the internet the quality of on-system help documentation has stagnated.