Well, set up your favorite form of an equation of a line. It should probably have an x, a y, and two or three more variables (parameters) in it. The fact that the line passes through (2,-3) should give you an equation and/or some other fact about the parameters. The fact that the line is tangent to that parabola should give you more information.
Alternatively, find the tangent line to the parabola at a general point, and see which of those lines pass through (2,-3).