Applied online and got an reply within 5 work days. Had a phone interview first. Normally it is the center director interview you, not the HR department. After pass the phone interview, I did a 15 minutes demonstration class. Using a non-English language to teach this language. For example, using Spanish to teach Spanish. You can choose any language you want to teach, but you have to speak this language. My suggestion is to not explain too much but have different activities; keep the demo fun and iterative. PS, they might give you an evaluation form before you lesson.