The images layer feature is an advanced way to create a custom product. It lets you add masking function to your custom product image and make the product color adjustable. The traditional way to make the product color editable is to create multiple variants for the product and assign an image for each variant.
A sample for a product that uses multiple variants:
Some sample products that use the images layer method:
Please find following a tutorial video of how to create layered images:
You can hire any photoshop expert to create the layered images as it is very technical.