Guide:New player guide
From The ESOC wiki for Age of Empires 3
Game version
Most players play Age of Empires 3: Complete Collection. This includes the basis Age of Empires 3 game (often referred to as vanilla), the expansion The War Chiefs (TWC) and the expansion The Asian Dynasties (TAD). Age of Empires 3: Complete Collection can be bought on Steam. This guide will assume you have the base game with the two expansions installed.
Playing multiplayer
Most people play multiplayer games using the official multiplayer platform ESO (Ensemble Studios Online) which you can find via the Main Menu > Multiplayer > ES Online (ESO). You login on this platform using your ESO account, which is separate from your Steam account. It is also possible to play multiplayer games using Voobly or Gameranger.