When I create a sales order, I can specify delivery method. And when I create a shipping record (packages, not shipped - ship - ship manually), I can specify carrier. Delivery method and Carrier seems to refer the same database but they're not related; I suppose the latter should be filled by the former automatically, as they should be the same content.

Also I suppose "delivery method" field should be in the package slip. It looks unavailable although it is said to be available here.
https://zohofinance.uservoice.com/forums/294735-zoho-inventory/suggestions/10535238-package-slip-needs-ship-to-carrier-fields