Objects and their properties appear on the timeline once they have been keyed. There are a few different ways to key a property. You can change the property on the stage, change the property in the inspector, or key the current value by using the key buttons in the inspector.
Keyed objects each appear on a single row of the timeline. Expand each object to reveal additional rows for each keyed property. The keys for each of these properties appear on the right-hand side.
You can change the key's position on the timeline by clicking and dragging it to the desired location. Use the grey keys to move all of the keyed properties of an object or use the blue keys to change a single property's location.