scaning concept

hi friends.
i m quite new in field, i could not understand what is scaning. can u brief me what is the basic concept of scaninpls

1. Go to Phil's tutorial (See 'Online Tutorial'), read at least the section titled "Theory Of Operation". Pay special attention to the sub-section "How It Works"

2. After that come back and post any questions in the "Live Questions and Answers" section.

Good Luck