Each WooCommerce order is independent in the sense that there is no way to bundle orders logically. At most, orders can bundled together based on their status and on the customer that placed them (as long as said customer also opted for creating an account). But this type of taxonomical bundling doesn’t always tell the whole story behind an order.
The Linked Orders for WooCommerce plugin aims to provide another dimension to bundling orders, namely based on relations that new orders have to already existing ones. For example, a warranty extension order that comes in 1 month before the warranty expires, or 23 months after the original order (assuming the default warranty lasts 2 years).
Types of linked orders
Orders that have no connection to others are called root orders. These are independent orders with no history behind. A customer can have any number of independent orders.
Orders that have a logical connection to another one are called child orders. These orders only exist because they are somehow related to a root order, directly (level 1) or not (level 2 or higher).
Every child order must have a parent order. In case of level 1 children, the parent order is always a root order and for the rest, another child order. Root orders do not have parents.
A parent order can have any number of children orders. A child order must have exactly one parent order.
How to create linked orders
You can create linked orders manually using the user interface provided by the plugin (read more about it here). You can use create orders programmatically and link them using the plugin’s API (read more about it here).