You have to apply via a a public advertisement that is usually broadcast on their website and sometimes in a public newspaper. Everyone who applies that fulfills the the criteria as specified in the advertisement is called for the interview. Interview can happen in person or via Skype depending upon the situation. Depending upon the the number of candidates you will have either one or two rounds of interviews. First round will be a short 15 minute interview followed by a longer and more in depth interview for 30 minutes,