Sinuous means winding or curvy. If you get lost on a sinuous mountain path, you'll need a compass or a GPS to figure out which direction leads back to camp.
The adjective sinuous comes from the Latin word sinus, which means to curve or bend. If you have a sinuous body, then you have lots of curves. Snakes use sinuous movements to travel. Live Oak trees have particularly sinuous branches. We usually use sinuous to talk about physical shapes of bodies or pathways, but you could also describe someone's logic as sinuous if it wanders all over the place when they're trying to explain something.