What are Advanced Product Types, how to enable them, and how to use Parent and Variant products.
Product Types help you differentiate and create relationships between your products. ShipStation has three product types to choose from:
Standalone: An individual product that is unrelated to other products.
Parent: A non-sellable product that acts as the primary product for reporting purposes, and contains the variant products that belong to it.
Variant: A sellable product that belongs to the Parent product and inherits any product defaults set in the Parent product details.
By default, all products are Standalone products. This just means they have no relationship to other product records in ShipStation. For reporting purposes, however, you may want to group certain types of products together.
By using Parent and Variant product types, you define certain products as belonging to another product so they inherit certain features by default.
Let's say you have a Hotdog T-Shirt in various colors and sizes. Currently, ShipStation treats those shirts as individual Standalone products for reporting purposes.
If you group all the different shirt sizes and colors available as Variant products under a Hotdog T-shirt Parent product, your Product Sales and Item Demand Summary reports can tell you how your new Hotdog T-shirt is doing overall.
Below is an example of a Parent/Variant hierarchy for our example Hotdog shirts:

Additionally, some product-level settings (like shipping defaults or reporting categories) get passed down from Parents to their Variants.
Here's a screenshot of a Variant product's Shipping details:

This shows the Domestic shipping information has been inherited from the parent.
Note
You can override any inherited shipping settings by setting the Variant's Defaults in the Product Details screen.
Ideally, your Products tab in ShipStation will already contain your existing product records. If not, review the article about importing products into ShipStation.
These product records will be Standalone products. Standalone products cannot be converted into Parent products (remember, Parent products are non-buyable products and they should have a unique SKU). You will need to create the Parent product in ShipStation, to which you can then add Variant products.
If you wish to create variants of products that already exist in ShipStation, you can also use the Combine Products option.
If you have many Variant SKUs to add, do a Product CSV import to create them all at once.
In the CSV, set a product as a Variant by adding its Parent SKU to the ParentSKU field, as shown in this example:

If the SKU you enter into the ParentSKU field in the CSV does not currently exist in your ShipStation account, a ParentSKU will be created for it when the CSV imports, as long as that SKU does not also occupy its own row in the CSV.