This circuit adds together all of the voltages put into it. The voltages are set to 3, 3, and 4. Making an output sine wave of 10V. It is really fun to mess with the frequencies instead though. It is really easy to understand the circuit if you understand the math behind it. This is where I learned this from. I hope it helps.
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/averager-summer-circuits/
