In class B amplifier transistor conduct only for half cycle of input signal.One conduct in positive half cycle and other conducts in negative half cycle.
Transformer T1 is called as input transformer called phase splitter and produces two signals which are 180 degree out of phase with each other.
Transformer T2 is called as output transformer and is required to couple the a.c signal from the collector to the load.
When there is no input signals both the transistor Q1 and Q2 are cut off hence no current is drawn from Vcc supply. Thus there is no power wasted in stand by the power dissipation in both transistor is practically zero.
During positive half cycle ON Q2 OFF and at the output half cycle is obtained Q1 during negative half OFF and Q2 on hence another half cycle is obtained cycle Q1 at the output.
Then output transformer joins these two halves and produces a full sine wave in the load resistor.