Well, there's just a ton of variations for this. Let's use the general equation and take the example of a train approaching the station at 25 m/s while a passenger is running towards the station at 5 m/s. The train whistle is at an annoying 750 Hz.
f' = f[ (1 +- vo/v) / (1 -+ vs/v) ]
here vo = observer velocity, vs = source velocity, v = speed of sound (which we'll assume is 340 m/s). The first sign is for motion towards the object, the second sign is for motion away.
So, armed with that knowledge both are towards each other)
f' = (750)[ (1 + 5/340) / (1 - 25/340) ]
f' = (750)[ 1.147 / 0.927 ]
f' = 928 Hz
Of course, you can also have mixed cases, such as the observer moving away from the source while the source approaches him. In that case you would use the appropriate sign (upper for towards, lower for away) corresponding to Vo (observer) or Vs (source).
Standing waves.....
Again, a standing wave can be described as a fixed (resonant) vibration pattern on a string or in a tube.
For now we'll talk about tubes:
a tube open at both ends has possible amplitude vibrations that looks like this: