In order to create a composite type of product, all you need to do is to create your product (just like you regularly would).
Now, moving down in the “Product Data” section, you can choose “Composite Product” from the drop down menu:
At the moment of the selection of the composite type of product, two options are going to be added in the upper area of the tab: “Per-item Shipping” and “Per-item Pricing”:
The “”Per-item shipping” option allows you to calculate the shipping costs based on the shipping properties (weight and size) of each component, otherwise (by deselecting it) the “Shipping” tab is going to be displayed, where you can specify the details for the whole lot.
Similarly “Per-item Pricing” allows you to add the price of each single component chosen by the user to the listing price. By deselecting it, only the price of the composite product is going to be used.