In Divergent, the people of Chicago are split up into 5 factions. Our main protagonist, Beatrice lives in the peace loving, selfless faction, Abnegation.
I don't think I'll be ready for the cermony.
After taking a placement test, and finding out she's been placed into three different factions (Normally only placed in one). At the choosing ceremony, she chooses to be placed in the Dauntless Faction, the fearless.
I choose Dauntless over Abnegation
After boarding a train to Dauntless, they jump off (Literally) on a building and from there, jump down a hole into the facility. From here Beatrice, now called Tris meets Christina and Will, as well as Peter, her soon to be rival.
Nice to meet you Beatrice, I'm Christina / Will..
Tris meets Four, one of the leaders of Dauntless, who only has four fears. He explains to the new trainees, that there will be 3 test they will put them through to see if they are worthy of entering Dauntless.
Each test will be harder than the last.
Tris goes through each of the test, each involving a new type of test. One about using weapons and defeating someone in a fight, one is about facing your fears, and the last is about using the skill they've learned to over come their fears.
Surprised you even lasted this long.
After completing the three trials, all of Dauntless is injected with a "Tracking Serum. In reality, it's a mind-control serum, that turns everyone except Tris and Four, in mindless soldiers. They who shut down the program and escape.