Answer to Question #31700 in Electric Circuits for sevag

Question

i have done a simple led dancing circuit , where i used 9 leds (in parallel) , common emitter transistor and a resistor , battery and phone(for AC source) its working well ( the transistor is used as a switch), but my question is about the connections of the circuit , 1) why is the emitter connected to the ground 2) the collector to the negative poles of the led and 3) the base to the positive of the leds 4) why is the resistor connected to the base of the transistor and its other terminal to the positive poles of the leds
?