Learn Zombies vs Humans in a few guided steps: your first cities, your first army and your first march, before you meet another player on the map.
The real interface, against a scripted horde: raise a city, feed an army, hold the walls, read the battle, take their camp and found a colony on it.
It opens by itself the first time you sign in, and runs again from here as often as you like. When you are done with it, the field manual has the rest.