Give a duration to your clips
There are two ways to give a duration to your clips.
The first method consists in editing each image's clip in the Clip : Layers tab and repeat it as many time as you need.
The second method, more simple, consists to stretch each clip by using the timeline view in the Project tab.
This method allows you to give rhythm to your animatic without spoiling the number of images that compose your clips. For example, if your clip contains 4 images, stretching your clip will not create new images.
The duration given to each clip appears in the right corner at the top (in thumbnails, columns or rows view) or at the bottom (in the timeline view). You can choose to display the timecode in images or in seconds.
Once your animatic is done, click on the play button to see the result.
Be careful, you can see the wholeness of your animatic only if you are in the Project tab. If you are in the Clip : Timeline tab, you will see only the animation of the clip.