To display products on a homepage (for ex. category “on Sale”) you need to open necessary CMS static block or CMS page. 

 With the following code paste the product list (list.phtml) to the page indicating the product category:

Where: 

category_id — Id of the category, which products you need to show. 
template — the template which will show the products, by default it is catalog/product/list.phtml, but you can create your own.