The pilot reported that while taxiing a tailwheel-equipped airplane down a slope the airplane began to slide sideways and the empennage turned downslope. Despite the pilot’s control inputs, the empennage reached approximately a 90-degree angle to the desired direction and the airplane tipped to the left. During the accident sequence, damage was incurred to the left wing and left horizontal stabilizer. The pilot reported no mechanical failures or malfunctions with the airframe or engine prior to the accident. The pilot stated the accident could have been prevented by obtaining more knowledge concerning the airstrip.