A1: You can see a power jumper(MB_EN) on the motor shield. If you move it, the Arduino can provide power to Shield, but the shield(if the shield has connected to a external power) can't provide power to Arduino.
If the jumper exists, one can provide power to the other under two situation:
1)USB to Arduino: if no external power connected to Shield separately, the Arduino will provide power to Shield via VCC pin.
2)External Power connected to Shield：If shield has a separate power, the voltage would through a rectifier(78M05) first, and then provide power to Arduino. At this situation, no current of Arduino could through Arduino to Shield via 78M05.
So the purpose of this jumper is a choice whether you would wanna use shield to provide power to Arduino or not.
Q2: Is there a pin conflict between the SD card shield (103030005) and the Motor shield (105030001) on Arduino UNO? How to use them together?
A2: There is a pin conflict between Motor shield and SD card shield in digital pins D11,D12,D13 of the Arduino Uno. So you cannot stack them together with the Arduino Uno board.
A solution to use them together is
1.Stack the SD card shield to the Arduino.
2.Modify the library of Motordriver.h as follows.
#define MOTORSHIELD_IN1 8
#define MOTORSHIELD_IN2 7
#define MOTORSHIELD_IN3 6
#define MOTORSHIELD_IN4 5
#define SPEEDPIN_A 9
#define SPEEDPIN_B 10
3.Do not stack the motor shield but make connections separately as follows from the Arduino using jumper wires.
Arduino Motor shield
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