Motion Sketch is a feature in Adobe After Effects that allows you to record keyframes for the movement of any layer with your mouse in real time. This is why it is called 'Motion Sketch': you are literally sketching the motion of an object in your scene.
To see the Motion Sketch panel, go to the main menu and select View -> Motion Sketch.
The Motion Sketch tab will appear in one of your panels on the After Effects interface. Motion Sketch is pretty simple and offers only a small set of options:
Note that the Start Capture button will be greyed out until you have selected a layer in your composition.
Now that you are familiar with the available Motion Sketch tools, let's use them to animate a layer in our composition!