This is the biggest, most high-stress competition in FIRST. In early January, students are introduced to an brand-new game every year and have six weeks (the "Build Season") to create a robot that accomplishes specific tasks to try and win the game. Teams are typically placed onto random alliances of three during qualifying matches, where they compete to make it into the finals. In the finals, teams get to pick their allies (this is where scouting comes in).
Last year, FIRST changed their model for competitions so that they are organized by "district," small meets that teams from around the area compete in. A team can compete in multiple district meets to increase their chances for making it to the larger, regional championship competitions. Teams can eventually advance through the regionals, and into the championships, held each year in St. Louis.
This year's game, introduced January 3rd, is called "Recycle Rush." The video below explains basic gameplay.