Cen'gar is a world filled with lava and molten rock, resembling the Firelands. The fire elementals here are being corrupted by the Burning Legion. In Legion an Invasion Point connects Argus to this target location.
Where to start? Well, somebody would say all the way back to Warcraft I (aka Warcraft: Orcs & Humans or the First War), or maybe Warcraft II (aka Tides of Darkness or the Second War up to and including Wrath of the Lich King, Warcraft III is the best place to start. Also, this game then elicits more interesting questions. For instance, how Illidan Stormrage became so hated or where the Scourge started. You will learn all the history and geography of the Warcraft with our help and dedication.