Use a right triangle: sine of an angle = opposite side / hypotenuse
Use a unit circle: sine of an angle = y-coordinate of the point on the circle
Use a calculator: enter the angle and press sin
Use a trigonometric table: look up the sine value for the angle
Use the identity: sin(θ) = cos(90° − θ)
Use known special-angle values:
sin(0°) = 0
sin(30°) = 1/2
sin(45°) = √2/2
sin(60°) = √3/2
sin(90°) = 1