How to make it. Adding arrows
If you’re referring to the standard image gallery in Sparkle, the arrows are already part of the object.
Just click on the object and add your images through the style panel.
If you’re talking about a horizontal scroller, such as the one illustrated HERE, you can use third-party code which you add to your Sparkle page through the ‘embed’ object. If you check out the example, you will be able to download the code and try it out - full instructions are on the example page.