Vlad Tenev is co-founder and co-CEO of Robinhood, a mobile app that lets you trade stocks free of charge. It's only a few years old and millennials are all over it – the average age of the app’s two million users is 30. The latest fundraising round valued Robinhood at $1.3 billion, with backers like Snoop Dogg and Marc Andreessen. But it took a lot for Robinhood to get where it is today, which Tenev explains in this episode of "Success! How I Did It" with Business Insider US Editor-in-Chief, Alyson Shontell.