The invation to interview was communicated by email. The time and location was listed in the email. the hiring supervisor was the interviewer. He ask how I heard about the postion. I was also aked if I was familiar with the postal mailing system.

Very easy. Come prepared, (bring paperwork, dress business casual- it may be a casual work environment, but you should treat all interviews professionally). Pay attention to your email as this is how they will communicate with you regarding the process, interview, drug testing time constraints and location information, your acceptance and so forth.