Adding slider images to my theme

I am trying to add the slider images to my theme and not sure how to do so in the wordpress backend. (here is the demo of the theme I’m using: https://livedemo00.template-help.com/wordpress_33417/)

The slider.php file is below. There is a “Slider” post section in WordPress and when I click “Add New” there is a “Custom Fields” section. I’m not sure how I’m supposed to add the images using the Custom Fields. Please help!

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