Something protruding is sticking out. When you're playing hide and seek, be sure your whole body is under the bed — a protruding arm or leg will give away your hiding spot.
The part sticking out of an otherwise flat surface can be described as protruding. If a display is protruding from a storefront, you have to walk around it. If you have a big, red zit protruding from your forehead, you should probably see a dermatologist. And if you look up the mountainside and see rocks protruding, look out! Protruding rocks tend to fall down, which could put a damper on the hike.