I need help with Tweening

programming flash
1

Hey everyone im kinda new at tweening. Below is my code all i want to do is an easeIn on the move. I know i simple but help would be amazing thanks in advance.

moveLeft.onPress = function() {
rocket._x +=500 ;
if (rocket._x > 0) {
rocket._x = 0;
}
}
moveRight.onPress = function() {
rocket._x -= 500;
if (rocket._x < -4500) {
rocket._x = -4500;
}
}