Document variables: lookup fields

Good afternoon! Tell me, how do the variables of the reference fields work in document templates? When forming a document in the process, we need to extract the value of the "Acts on the basis" field from the reference book, depending on the "Legal entity" field filled in in the process, here is the reference book https://crm.ohrana.ua/admin/shop/custom/object/ directory/10/ (it's with standard Wallets and Accounts automation) The process for the test https://crm.ohrana.ua/admin/customorder/bukhgalteru/524121/edit/ , document Agreement, the legal entity of the process is filled in (it is also the Legal entity field in the directory), the document has a directory field {row: directory10_deystvuetnaosnovanii } Please describe the functionality, how to apply. Or do you still need to link the fields of the directory with the fields of the process and fill in the fields of the process? Then what is the functional of these variables. Thanks