Practice practice practice. It's like learning guitar, ya gotta keep doing it to get any good at it.
Don't get nervous about other drivers. They all have brakes and know how to use em. Plus, they'll automatically know that you're an inexperienced driver just by the way you're driving (or they'll think you're drunk :)

And if your instructor yells at you, yell back and tell her in no uncertain terms... "Do not yell at me while I'm driving!!". If she can't get it through her thick head that she's making things more dangerous for you, ask for a new instructor and complain to her supervisor. Nobody has the right to treat you with discrespect... especially a teacher.