My interviewer explained it as glenda did above.
Most of the time you are taking pictures for guests at character meet and greets and in front of memorable icons (the castle, expedition everest, etc). Pretty much anywhere you would walk past and be like "Oh this would make a nice christmas card", photopass is there for you! If you're the first photopass photographer a guest has encountered, you give them a photopass card. They keep this card for the entirety of their trip and hand it to each photopass photographer before they have their picture taken or before their character interaction. The photographer swipes their card (similar to a credit card machine) on a piece of equipment connected to the camera and gives the card back, then takes their pictures. When the guests return home, they go on the photopass website and all their pictures are in an online gallery where they can order prints, cds, and photopass merchandise (shirts, mugs, calendars, etc).
In addition to taking pictures for guests, you'll be manning photopass kiosks and booths and selling photopass merchandise which would be like mugs and tshirts with pictures from their photopass cards. This is unrelated to things like on-ride pictures.