I need a explain

Simply add a switch in series to generator, start simulation with switch opened then close switch to start simulation of multivibrator

The circuit works by the voltage pulse of one transistor is added to the biasing voltage of the other transistor thru the interconnected feedback capacitor, when that happens the transistor changes state it then changes the other transistor to the opposite state, and so on the frequency of this occurrence is determined by the RC time constant of the base components. The self starting ability of the circuit depends on the stability of the circuit, the closer the circuit is to it instability point the easier it is to start. This point is determined by two things 1 being the ratio of base current to collector current, if a transistor has a gain of 100 as the default transistor in EC has, the base collector current ratio should be close to100, 33k base resistors would do that for this circuit. (it will change the frequency, so if this is important the capacitor value would have to be changed also). The second being the closeness of components in being mached, a slight difference (which is fairly normal) makes starting easier. There is a slight symmetric error in this circuit not that it matters much, but the bottom capacitor could be connected to directly on top of the left transistor to balance the circuit.

Your circuit, adjusted; http://everycircuit.com/circuit/5216511489998848

cambio de valores(?)