Single Wave
Set the amplitude of the second wave to zero by sliding the slider all the way to the left. This is the default, so it might already be there. Now try varying the amplitude, wavelength, phase, and direction of the first wave and seeing what happens.
Interference
The third wave above is the sum of the first two and thus can be used to illustrate interference effects. First, try setting the amplitudes, wavelengths, and directions of the two waves to be the same. Also set their phases to zero. The third wave should look the same as the first two but have a large amplitude. This is constructive interference.
Now, change the phase of one of the waves (either one) to 180 degrees. As the phase changes, the amplitude of the sum wave should decrease until it is zero at a phase difference of 180 degrees. The two waves are now cancelling each other out. This is destructive interence. Try also random changing the amplitudes, wavelengths, phases, and directions of the two waves (different values for each wave) and notice what happens to the sum wave.
Beats
Set the two amplitudes, phases and directions to be the same. Set the wavelength of the first wave to 0.4 and the wavelength of the second to something close, say, 0.47. You should see a beat pattern. Try changing the second wavelength slightly and notice what happens.
Standing Wave
Set the two amplitudes, phases, and wavelengths to be the same (try something around 1 for the wavelengths). Give the waves opposite directions. The sum wave should now be a standing wave. Change the amplitudes, phases, and wavelengths (keeping them the same for the two waves) and note the effect on the standing wave.