Hi,
I assume you mean the Camera?
Perhaps the easiest way to have the camera zoom in on a moving object is to parent the camera to the object you want to zoom in on.
It will then follow that object anywhere it goes but can be moved independently of that parent object.
In this way we can have it start from some other location... track the object... and zoom in or out anywhere along the way.
There are other ways as well, such as by using expressions but in this case that doesn't seem necessary.
-Rodney