I assume that you are using the Curve by Equation command.
When you write an equation for a Cartesian coordinate system (you have to reference a coordinate system), it is written in terms of x, y, z, and t. The fourth variable t changes from a value of 0 to 1 over the domain of the equation.
Therefore for a sine wave, try the following:
x = 360 * t
y = sin(360 * t) * 100
z = 0
The value for y is multiplied by 100 only so that the x and y axes aren't disproportionate to each other. (It's a scaling factor.)