This circuit demonstrates an amplifier stage with common-emitter transistor topology and negative feedback formed by 150 ohm resistor placed at the emitter of the transistor.
If you compare the shape of waveform between input and output of the stage, you can note it is almost the same. It's because of the negative feedback action.
As always, there is a trade-off between an amount of negative feedback and the overall voltage gain of the stage. The stronger negative feedback, the lower overall voltage gain you'll get.
An overall voltage gain of the stage is slightly over 20.
