Can someone explain it to me...?

i got this code to make my character move when the mouse is clicked, but im not sure how it works.

onClipEvent (load) {
clickSpot_x = _x;
clickSpot_y = _y;
speed = 4;
}
onClipEvent (mouseDown) {
clickSpot_x = _root._xmouse;
clickSpot_y = _root._ymouse;
}
onClipEvent (enterFrame) {
gotoSpotX = clickSpot_x;
gotoSpotY = clickSpot_y;
delta_x = _x-gotoSpotX;
delta_y = _y-gotoSpotY;
targetRotation = -Math.atan2(delta_x, delta_y)/(Math.PI/180);
_rotation = targetRotation;
if (Math.sqrt((delta_xdelta_x)+(delta_ydelta_y))>speed) {
_y -= speedMath.cos(_rotation(Math.PI/180));
_x += speedMath.sin(_rotation(Math.PI/180));
}

}

if someone can tell me why it moves i’ll be very thankfull