In order to create a multi part product you must first have created a product (covered in a previous article). Once your product has been saved with the necessary information go to Catalogue > Product Types > Multi Part Products
...and click "Add New"
From here, you can decide which product the Multi Part Product will be based upon and whether or not the user can have the option to upload their own file.
Once this has been saved, you will be redirected to the Multi Part products page where you can see the entry for the product you have just created and configure further options by clicking Edit on the far right.
On the Edit page you can set the price per page of the editable product and edit the product's XML configuration (for advanced users)
Congratulations you have created your first Multi Part product!