2P means drawing a circle on the basis of two points on the circumference. 3P means drawing a circle on the basis of three points on the circumference.
3P Method: Initially go to the menu Draw>Circle>3 Points. Then the command prompt will send notification as _3p Specify first point on circle. This is just notifying you to select a point on the screen that will be your first point. Then AutoCAD will send notification to Specify second point on circle i.e. choose another point to draw your circle.