1: As the solar cell receives light, it generates electrical energy, which is absorbed by the 3000uF capacitor.
2: Once the capacitor is charged with enough voltage that the FLED can be triggered, it does so, thus also providing the necessary base current for the 2N3906 to activate.
3: the collector of the 2N3906 sends an amplified current to the 2N3904 which in turn amplifies again the current and draws a large amount through the motor, causing it to spin.
4:The voltage on the capacitor begins to drop because of the large current consumption of the motor which the solar cell is not capable of constantly maintaining.
5:The voltage goes below the minimum needed to keep the current flowing through the transistors, de-activating the circuit until the solar cell again charges the capacitor to the sufficient voltage to activate the FLED, restarting the whole process.
note: since the 3000uF cap is connected in parallel with the rest of the circuit it does not impede the current flow to it. it's purpose is to store the energy from the solar cell over a length of time and then release it in a quick burst.