The timer IC(NE555) is wired as an ASTABLE MULTIVIBRATOR in this circuit. It will generate Alternating non sinusoidal output wave form at the instant we giving supply Voltage(12V). Thus primarily we generated Alternating Voltage from direct Current (Battery). The output from these transistors are again fed to the input(primary) of a Stepup Transformer.
This will upconvert the input Voltage to desired level (230V).