A carousel shows one item, or a few items, from a group and lets someone move to the next or previous one. It is like turning pages in a small picture book without leaving the current page.
For example, a product page might let someone browse several photos of the same item. Arrows or clear controls let them move through the pictures, and a small position marker can show which one is currently visible.
Do not make essential information available only in a carousel that moves by itself. People should be able to control the movement and understand how many items there are.