Today's (June 22nd 2017) Google doodle is basically a sequencer, meaning there is a time grid that you can put musical notes onto that will play when the sequence comes to those notes.
The doodle is a fun musical toy. You get 4 instruments, one sounds like piano and the other three sound like bells of various sizes and shapes. And you get a large grid. You use your mouse to put a tick on any spot. Then a cursor moves left to right across the grid. As it reaches the spots where you've put a tick, it sounds.
You can make chords or melodies or both. Once you've putin some notes for one instrument sound, you can change the instrument. Your original notes aren't visible anymore because the fresh grid allows you to put marks in the same note-time grid point. The original notes do continue to play though. So as they do, you place new notes/chords with the new instrument and both will play at the appropriate time (when the cursor reaches them).
Repeat the process for the 3rd and 4th instrument and you can create something pretty darned cool.
The doodle was to celebrate Oskar Fischinger's 117th birthday.
Who was Oskar Fischinger? He was an artist. One of the things he loved to do was combine music with his art, making musical animations. He did not invent the sequencer:-P. It just so happens that using a synthesizer-type sequencer like this, you can create musical animations like Oskar Fischinger's.
You can only play the synth on the normal Google page today (June 22nd, 2017). So go play. If you're reading this after the 22nd, go here to check it out: https://www.google.com/doodles
If you want to read more about Oskar Fischinger, click here.