Creating An Assembly From a Sales Order.

Users are able to create Assembly Sessions directly from an open Sales Order by clicking on the Create button and selecting Assembly Session.

For products setup as assembly, you can create an assembly session directly from the sales order which will tie the two records together and scheduled the assembled quantity on the order. 
You can do this on a sales order by clicking + Create... > Assembly Session
When the assembly session is finished the product will be allocated to the order. If the assembled product is lot controlled, then the lot numbers will be auto allocated to the order. 

If the assembled product is needed on another outstanding order, then the full quantity of the assembly may not be allocated to the sales order that the assembly was built for. You can get around this by manually setting the scheduled quantity.