R1 and R2 bias the transistor in class A, so that a steady collector current flows. R3 is the load resistor. Look at the signal into C1.
During the first half cycle it is positive, and increases the forward bias on the base of the transistor.
This increases the base current and thereby the collector current through the load resistor. Therefore the voltage across the load increases, and the collector voltage, with respect to the zero line, decreases. The collector voltage falls as the base voltage rises.
During the second half cycle, the input signal goes negative, reducing the forward bias on the base. This reduces both base and collector currents. The voltage across the load resistor falls and the voltage on the collector rises. Again, the collector voltage has done the opposite of the base voltage.
The transistor inverts the input signal as well as amplifying it.