See this page for general information about creating documents.
"Items to Pick" is a Formset
See the "Formsets" portion of this page for details on how to work with formsets.
Associated Document
When the picks are made for a pick sheet, the inventory transactions will be associated with a document. If you enter a document in the "Associated Document" field, this document will be the one associated with the picks. For example, if you are creating a pick sheet for parts for a work order, you would enter that work order into the "Associated Document" field. If you do not enter a document in the field, when the picks are made they will be associated with the pick sheet itself.