Gather gold from mines and lumber from forests with workers. Build farms for food, a barracks to train soldiers, and destroy every enemy building and unit.
Humans of Aldmere: Footmen, Archers, Knights, Ballistae and Mages (Fireball, Mend). Stone buildings, guard and cannon towers. From the Eyrie: Roc Riders and bomb-dropping Skyships. From the Shipyard: Cogs, far-seeing Frigates and Bombard Galleons.
Orcs of the Bloodfang Clans: Grunts, Axe Throwers, Wolf Raiders, Catapults and Warlocks (Rot Cloud). Tough grunts. From the Bat Roost: blood-drinking Dire Bat Riders and fire-breathing Drakes. From the War Wharf: War Rafts, ramming Reavers and pitch-hurling Siege Barges.
Aliens, the Xenith Brood: Warriors, Spitters, Stalkers, Ravagers and Matriarchs (Brood Frenzy). Every creature and hive structure slowly regenerates; they are fast but lightly armoured. From the Wing Hatchery: pack-hunting Razorwings and Latcher-laying Spore Mothers. From the Tide Nest: Brine Crawlers, submerging Razorfins and the Leviathan.
On Lakeland and Inner Sea maps every base has a shore. A second-level hall and a lumber building unlock a harbour, which must be built touching open water. Ships sail only on water and the shallow fords that armies wade across; they can be hit by anything that can reach a ground unit, and only the fast warships can shoot upwards. Transports carry six berths of ground units: right-click one with soldiers to board, right-click a shore to unload. Ships moored beside their harbour are slowly repaired.
Once your hall reaches its third level you can raise an aviary and take to the air. Flyers cross water, forest and walls, never trigger traps, and only ranged units, mages, flyers and arrow-type towers can hit them: swords, cavalry, siege engines and splash towers cannot. A base with nothing but footmen and cannon towers is defenceless against them.
Every race can raise a Portal once it holds a third-level hall and a temple, and it is ruinously expensive. Build two and they link: any ground unit that walks onto the dais of one steps out of the other, in either direction, and the pathfinder uses the way whenever it is shorter. The gate is open to everyone, friend or foe, so a portal pair is a shortcut for your army and a back door for theirs. Only two may stand at once; if one falls, the other goes dark until it is rebuilt. Flyers and ships never use them.