let's recall on the Unit circle that, as the angle opens opens opens, the "y" value goes up up reaches 1, the as the angle continues it goes back down down and so on.
to make it short, sin(θ) just as cos(θ) will always spit out a value that is either -1 or 1 or anywhere in between, thus their range is -1 ⩽ sin(θ) ⩽ 1.