Different regions are at different levels of Maplestory progression and thus the older guide sections are kept. Explorers and Adventurers are the same thing. GMS uses Explorers, KMS uses Adventurers. If you are in GMS, you only need to look at guides for Ascension for now. When we get Justice, there will be new guides needed, particularly for Thieves, Pirates, Phantom, and Jett.