You have to go to your pc or desktop and make an application with italki, before you make an application, check if the language you want to teach is open for application, you choose if you want to be a professional tutor or community tutor. follow the application and fill it up, the waiting period is within 10 days after you submit, once you are pre-approved they will tell you what to do.

Scroll down to the bottom of the page and click the link that says "become a teacher." You'll find all the information you need.