Think of MMOs more like sandbox games, while they usually have some background story, it is usually less developed compared to Single player games.
Not much linearity or definiteness of purpose, just a persistent world with lots of stuff to do, much of the challenge is usually set to levels and progression. That might give the game a little sense of linearity though.
Changes made in a game world are really simple using flagging systems. Ie: Player A saved village = true >>> show happy people cheering, change dialog set to "x-group" etc etc...
For each player the game tracks their achievements and sets the variables accordingly.
You don't need a guide, definitely not one that calls less experienced people "idiots", people new to stuff are not dumb, just go forth and experience some games you like by theme or description/ gameplay videos, etc...