Hi Ana,
After completing the first phase, you need to shoot a video of yourself while speaking the languages you're going to teach, and submit it to the Italki staff, which will decide whether to pre-approve your request. Then, after you receive an e-mail which confirms you've been pre-approved, you need to watch a series of short videos and answer some questions about the Italki rules (with a little quiz) and a survey.
After you've done it, you're left with the last step: you have to schedule a video interview with an Italki staff member, which will be approx. 45 minutes long.
If all goes well, you're in! :)
P.S. Obviously, if you wish to become a pro teacher, not just a community tutor, you must provide some official documentation to certify you're qualified to do that.
Hope it was helpful, cheers!