What
“Hacker101 is a free class for web security. Whether you’re a programmer with an interest in bug bounties or a seasoned security professional, Hacker101 has something to teach you.”
Part of HackerOne, a bug-bounty platform. You have to create a hackerone account to get started. I love their CTF (actually this was the first CTF I’ve tried). As you solve the challenges, you’ll get invitation points. For every 26 invitation points you collect, you’ll get a private invitation to a private bug bounty program on hackerone! After completing the first two challenges with easy difficulty (Micro-CMS_v1 and Postbook), you should already have your first invitation to a private program.
There are also a bunch of useful free video lessons for start with the challanges and bug bounty hunting.