Remember, Parent products are non-buyable "umbrella" products that exist to group variants for reporting and also to push product-level settings to their variants. Since it's not possible to buy a parent product, they can't be associated with inventory units.
Parent products will appear in your Products list, with their Variants nested below. If you have your stock related columns visible, your Parent product will display the total stock available for all related variant products, and the Variant products will display their individual stock counts directly in the Products grid:
Variant products are products under a Parent "umbrella" and can be configured with inventory, just like Standalone products. Inventory will be deducted from the individual variant products when you ship them.
Variant products will be nested under their Parent product in the Products grid. They will also display individually in the Inventory section of your Products tab. Parent products will not appear in the Inventory section.
As you ship the Variant products, ShipStation will deduct inventory from the Variant, and the Parent stock counts will decrease accordingly.
Aliases can be assigned to either Standalone or Variant products (but not Parent products).
When orders import with a SKU that is an alias of either a Standalone or Variant product, ShipStation deducts stock from the master SKU the aliased SKU is mapped to.
For more information about Product Types, and how to create Parents/Variants, please go to this help article.