The interviews are casual, but very thorough. It is important to the company that you fit into the culture and have drive and motivation to succeed. Eagerness to learn and better yourself is also important. There are 3 interviews total, one phone screen and two in-person interviews. The phone interview will go over your previous experience, why you want to work at this company, and why you want the position. It is also to screen your phone manner. The first in-person interview will go more in-depth about your previous experience and how you apply your experience to the position. It is also very much about personality at this point and what kind of management style you work best in. The second in-person interview will include a presentation, where HR gives you a question ahead of time and you must demonstrate the ability to clearly articulate technical knowledge. This presentation also tests your ability to learn technical knowledge and how you present this knowledge.
Make sure you are able to go in-depth with your previous experience if need be--they will catch any/all BS that you make up by continuously asking follow-up questions if they think you're lying. It is important that you ask questions and be yourself in these interviews as that is critically important to this company when hiring anyone.