There are two ways in which you can preview a scene in the editor; by manually dragging the cursor on the scene layer timeline or by playing the active layers using the play function.
The manual cursor dragging on the timeline is useful when you are working on animation of individual layer objects. You can then drag back and forth on the timeline to see how the animation is looking. When you feel that it looks right you shall use the play function to see that the timing is right. The play function advances time in the right speed as it will be shown in the Demorize Player. The play function also plays all the layers that have been activated, which is useful if you have separated your design into multiple layers.