There are 2 ways to insert motion point in the timeline of a layer.
A. Right-click (right mouse button click) on an empty frame, and then click 'Insert Motion Point' on the context menu.
B. Double click on an empty frame.
A motion point represents motion property values of a layer at a specific point in timeline.
Given a layer has 2 motion points P1 at 1 second and P2 at 2 second in the timeline. X of P1 is 70 and X of P2 is 100.
The layer will move from 70px to 100px in direction of X-Axis during the period between P1 and P2.
Select P2, set motion properties.