The picture shows a manual tank drain. It's knurled to provide you with better grip when twisting it off with your fingers.
It's a good idea to wear gloves. One reason is that you'll get a better grip and not hurt your fingers as much. Another reason is because you don't want to get the "water" on your hands.
The water that drains out of an air compressor tank drain is not clean. It's typically laced with compressor oil, dust from the intake filter, corrosion, etc. It'll come out brownish in color, and if you drain it onto your garage floor, it will stain the concrete. I recommend placing an oil pan or a small bowl or bucket under the drain so you can dispose of it appropriately.
To make sure your air compressor tank lasts longer, you can slow down corrosion and prevent rust-through by draining the condensation completely after every use. Don't just loosen the drain valve, because it can sometimes stop draining before it's empty. Make sure you loosen and completely remove the ring from the bottom so it can fully drain.