Unlike vanilla, you don't launch missions immediately. You must "Infiltrate" by sending a squad and waiting on the Geoscape.
You will fail your first LWotC campaign around August. You will lose your best soldier to a critical hit from a unit you couldn't see. Advent will drop a pod of Muton Elites directly on your extraction zone. The Chosen will daze your medic while a Priest Mind Controls your Grenadier. xcom 2 long war guide