To on the front page was a slider of sticky posts, you need to:

1. As a front page to assign a static page.

set front page in customizer

2. For a static page assigned as the front display, you need to assign the Front Page template (Page Attributes box: Template, on page editing screen).

setup front page

3. Assign Sticky* at least 2 posts with uploaded the Featured Image.

* How to Make Sticky Posts?
When you create a new post or edit, look towards the right hand sidebar where you will see a Publish box. Look at the (Visibility: Public) field and click edit. Check the box to make the post Sticky. Press Publish/Save.

enable sticky post

4. Check Slider Sticky in the Customizer Front Page Options.

customize-sticky