Moving over the input fields with the aid of Tab button enter the values of sound waves velocity, the first medium (where incident wave's propagating) density, and the second medium (which is the wave reflector) density in the format convenient for you: 24.78, 15E-3, 11e4 etc. Then click the Calculate button. Dimensionalities may be arbitrary, but must be equal for both media. Clicking on the Change medium button results in changing characteristics of these media. The first medium will get properties of the second one and vice versa.
As an example, here the data for the case of incident wave propagating through the air and impinging on the air-water boundary is represented (velocity is measured in m/s, density is measured in kg/m3).