What is the difference between Delete and Ripple delete?
Here is a short video that will help you understand the difference:
Right clicking on a layer will give you an option to either Delete or perform a Ripple Delete.
Deleting an element will simply delete it, leaving the space it was occupying on the scene timeline.
Using the Ripple delete option will delete the element and also the gap it leaves behind from the timeline.
The Ripple delete option will only work if there is no other element occupying the same space on the scene timeline.