Home Page Slider
You can add a post or page to your home page slider in Pages > Home Page (or your chosen name for this page) > Featured Slider > Click + to add a slide. You can use the link, image, title, and subtitle you prefer.
You can add post's to your blog's slider by checking the Display Post in Slider on the right-hand sidebar of your post's editor.
You can adjust your blog slider's settings in Appearance > Customize > Blog Slider.