Rule 15: Relief from LOOSE IMPEDIMENTS and MOVABLE OBSTRUCTIONS (including Ball or Ball-Marker Helping or Interfering in Play).
Loose Impediments are all those unattached Natural Objects found around the course such as stones, leaves and twigs. They can be removed from anywhere but if the removal of them causes the ball to move, the ball must be replaced under penalty of one. The exception being on the Putting Green when the ball must be replaced but no penalty will be incurred.
Movable Obstructions are man-made, artificial objects that can be easily moved without causing damage or delaying play, such as a water bottle or a rake. If the ball moves replace the ball without penalty.
If the ball is in or on the Movable Obstructions then you must mark underneath the Obstruction (plastic bag or golf towel) and the Ball. The Ball-Marker will be the Reference Point which must be in the same area of the course as the Obstruction and no nearer the hole. The Relief Area is within one club-length of the reference point, no nearer the hole and the ball must be dropped from knee height into the Relief Area and come to rest in the Relief Area without penalty.