When I come to a complete stop and then try to turn my vehicle it stutters and shuts?

Im sorry This is my boyfriends car, and Im not to familiar with cars lol. Let me try to rephrase the proplem. Im driving it down the road, and as I am comeing down a hill etc. And stop to wait for oncoming traffic to turn onto the highway first when I stop the car will seem to get really queit like its losing power. When its all clear for me to take off, I will begin to turn and sometimes it will completelty shut off and ill have to put in in park and restart it. Other times it will shake and putt foward a little bit and I will have to keep pumpming the gas until it finally decides to pickup and go. But this isent and all the time affair. I just dont know what I should do. I know some basics about cars but im know mechanic and my boyfriend is no help to me at all.