In order to add multiple versions of a product, you first have to define those attributes that will make a distinction between the different versions of that product (color, size, etc).
Go to the Product catalog menu - Attributes management, in order to add attributes. In the Edit page of each product, in the Product Options section, you have to select the attributes that you want to add to the product. The additional cost option allows you to set different prices according to the product version.
Listed in: Catalog settings