Using Arduino and Motor Shield I am a beginner in Arduino.I want to connect 2 motors to Arduino. 
Do I require a motor shield?And if yes please tell why?
Also can i use an amplifier to increase the voltage for the motors?

And one last important question, I have just seen the motor shield's pic. Does it restrict arduino's pin usage? I mean we can't use the arduino pins if we use the motor shield right?

PS: I am talking about this model: SLAEX039 L293D Motor Shield 

Thank a lot
Yes. To use standard D.C. motors, you must use a motor shield or the L239D chip. This is mainly due to motor noise, and control to run the motor at different speeds and directions. Also you get very easy to use libraries!