How to link master orders to sub-orders
Start by creating a new order, with description Master order:

The new order (in this case AWC-18 is created. Now select the Sub-orders tab which shows No sub-orders:

Next, select Create new sub order to create the actual new sub-order:

A new order (in our case AWC-19) was created and added to the table of sub-orders. It has the same creator and description as the master order; all other fields are blank. Now, select Add existing sub order to add an existing order as a sub-order:

In the sub-order edit form select or type an existing order's key, and click Save:

The existing order (in our case AWC-7) was added as a sub-order.
To see what master order a sub-order belongs to, navigate to the sub-order. In the sub-orders table, select sub-order AWC-19:

The details table shows Master order: AWC-18 Master order.
To change the master order to a different one, select Edit order details to change this sub-order's description and select a different master order:

Using Sub-Orders