Tony Xu grew up as the child of immigrants, working in his mum's restaurant before going onto Stanford and working at McKinsey, eBay and Square. In 2013 he started the food delivery service DoorDash, at first running the deliveries himself. Now his company employs 500 people, works with over 200,000 delivery people, and operates in 600 cities. We talked to Tony about how he runs it all.