Hey, I am not sure if I understand, you don't need to edit a template file to pull this off :)
open the wordpress backend and go to Levitation options-> mainpage options. choose one or more post categories at 'Levitation Starting Page Image Slider'
once that is done save the setting and create a new post. make sure that the post has applied on of the the categories choosen above. Also make sure that you add a image url to the input field thta says:
"Image for Slider/Portfolio Full Size". you should be able to find it below the textarea for post content.