the mask tracker is for tracking masks. it tracks the area you masked and does not apply transform data but only path and vertices data for the mask to move. There are some limited uses for this technique but it's used mostly to track an adjustment layer with the mask so that you can apply an effect to a certain area in the frame that's moving.
What you want to do is classic tracking - attach a layer to an element that moves, and for this you can use a different kind of tracker. highlight the footage you want to track and open the tracker window where you will see 4 options. What you choose here is dependent upon the nature of your shot. Track motion is the classic point tracker: you select a feature you want to track, specify a search region and start tracking. when you are done you can apply the tracking data to a null, then attach your image to that null (it can be masked or not). To learn all about Tracking it will take more than intuitively clicking here and there or getting answers in the forum. Type "Tracking" in the upper right search field of your Ae interface and you will get the official Ae's resources about it such as this: Tracking and stabilization motion workflows in After Effects
Maybe this will help. Sorry, there's no audio.
This is just one of several techniques that can be used to stick a layer to something that is moving in a shot.
You should spend some time studying the link that Roei gave you and read up. If you run into something unexpected then try the search help field at the top right corner of AE to find some documentation on the subject. Your first instinct was to use mask tracking so if you were my student I'd tell you to first read up on mask tracking by typing "mask tracking" in the search help field so you had some idea what it was used for. 2 minutes reading would have saved you 2 hours of wasted time.
If using most software is like driving a car and you can figure out how to get from point a to point b with a few minutes instruction from your mom in a church parking lot then understanding After Effects is like trying to learn how to land an F-18 off an Aircraft Carrier at night in a hurricane. You can probably keep your plane in the air with a few minutes of basic instruction on the use of the stick and rudder, but you're going to crash unless you have spent a bunch of time studying where all the switches are located and how to set things up for a successful landing.
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