Simple see the circuit circuit.
when u turn give 6v to circuit , current passes thru pnp emitter to base and thru 330k.
pnp tran. conducts and ,+6v passes thru pnp emitter to collector thru 1k to base of npn.
npn conducts . +6 pass thru 22r and upper led to npn collector , and collector to npn emitter and thru. led to -6v.
when npn collector conducts collector voltage reduces sharply ( the falling voltage is like a ac pulse )and what happens is that the base of pnp transistor that has about 5.4volts is shorted for a short time thru 10u capacitor to collector of npn voltage.
now there is no base voltage for a short time so pnp dis-conduct and npn after that and led go off, npn collector goes high and 10u cap has same voltage on both sides and no current passing thru cap..
so now once again there is base voltage 5.4volts on pnp (emitter is 6v) and pnp conducts again and once again starting what happened for the start "current passes thru pnp ...."
now try to understand what happens on the left circuit yourself.
good luck.