You should put your car in 4 wheel drive when you are driving on rough, slippery, or uneven terrain, such as snow, ice, mud, sand, or steep hills. 4 wheel drive can provide better traction and stability, which can help you maintain control of your vehicle and avoid getting stuck or sliding off the road. However, you should also be aware of the limitations of 4 wheel drive and adjust your speed and driving style accordingly. In general, you should only use 4 wheel drive when necessary and switch back to 2 wheel drive when conditions improve.