Something smooth is free of roughness, stubble, or other imperfections that you can feel with your hands. If your wooden table is giving you splinters, use a sander to smooth it down and make it smooth. As you can see, smooth works as both a verb and an adjective.
Smooth has lots of interesting uses: Caught in a wind storm? Better smooth out your hair when you head inside. Got a friend who's good with the ladies? Try imitating his smooth moves. Need help to smooth out a dispute between two friends? Invite them out for coffee and offer to help them smooth out their differences. Some pianists prefer ivory keys to plastic because they're less smooth, and their fingers don't slip. The best dancers can move smoothly from one move to another.