Facebook ads drive sales by creating demand at scale. The algorithm studies your buyers and hunts lookalikes, so CPA often drops as you spend more. You run awareness, retargeting, and checkout pushes in one platform with shared data. Post-iOS14, creative is the targeting — a strong hook finds the right people even on broad. You get ROAS feedback in 48 hours to kill losers and scale winners fast. Every campaign builds retargetable audiences that cut future CAC. Nail offer, creative, and data, and it turns into predictable math: $1 in, $3-5 out.