Operation Gatecrasher in XCOM 2 is the story's opening Mission.
Sabotage ADVENT Monument.
- Neutralize all enemy forces
- Plant X4 on the monument
Locations and specific parameters is randomly generated, but in this mission's instance the name of the mission and its objectives are always the same. Your starting squad will be tasked with sending a message to Advent by sabotaging a monument at a priority location in the world.
Move your units into tactical positions and eliminate the ADVENT enemies. This early on, grenades can be very effective at eliminating grouped enemies. Once the enemies are eliminated advance on the monument and use one of your units to plant the X4 from their action options on the monument. The X4 explodes and your mission is complete. Congratulations on striking the first blow in a long war!