Featured Post and Category slider is useful when you have to highlight your post as slider.
1. First go to your WordPress Dashboard and then Appearance - Customize - Featured Slider
2. in "Enable Slider on", you need to select either Homepage or Entire Site as per your need.
3. In Select Slider Type, you need to select the slider type as Featured Post Slider or Featured Category Slider
4. If you have selected Featured Post slider, then you need add in post ids and click on "Save & Publish" but if you have selected Featured Category Slider" then you need to select "Category" and click on "Save & Publish"