How to create hover changes?

You can only make layers appear/disappear on hover, but you cannot change for example the background image of the slide. Let's take a look at the options you have:

Rows and columns

By using row/col structures, you can use for example the column's style to insert a background image in it and also select a normal and hover background color.

Transition layer

By using transition layer, you can create a hover effect, where one image is displayed and on hover it changes to another one.

Caption layer

With caption layer you can create a hover effect, where one image is displayed and on hover a text appears on it.

Events

Layer events can be used to make layers appear/disappear. You should check out that documentation to understand how this works.

The main problem you will have with this option is, that you will probably want to have multiple layers on top of each other, to make the top layers appear (maybe the bottom layers disappear). To have layers on top of each other, you have to use absolute positioning for all of your layers. The issue with this will be, that absolute positioning has a lot of limitations: 

1. In a lot of cases you cannot position them to default layers properly, so you will have to use only absolute positioned layers everywhere, not just at this hovered part.
2. Setting up a nice responsive display is also hard, sometimes impossible.
3. You cannot make your layers cover the entire slide, while certain responsive options are used, like the Limit slide width.

But the freedom this option will give to you is, that you will be able to create any design, to make layers appear/disappear with any layer animation.