What are digital files?

There is a photo contest my daughter wants to enter, and in the instructions it states that only digital files will be accepted..what exactly is a digital file and how would I (I will be the one sending this off for her) make a picture into a digital file to send..would that be like a regular attachment to their form?...I have no knowledge of computer files or imagery so please tell me in layman's terms so I can understand. She has use of a Nikon D80 camera if that makes any difference. Thanks