"Owls make journeys."
Translation:Bubones itinera faciunt.
From a noun's listing, you can tell its DECLENSION and its GENDER:
The first word listed is the nominative singular: iter.
The second word listed is the genitive singular: itineris.
The fact that the gen. sing. ends in -is tells you it's a 3rd decl. noun.
Removing the -is ending from the gen. sing. gives you the noun's BASE, which shows up before endings: itiner- (inherited into English in "itinerant," "itinerary").
This noun is also NEUTER: iter, itineris, n., journey (would be the full "dictionary entry" for the noun).
Thus, as a neuter noun, its nominative and accusative (and vocative) forms are all identical:
Iter longum est. (nom. sing.) . The journey is long. Iter longum faciunt. (acc. sing.) . They are making a long journey.
In the plural, the nom, accus (and voc) of a neuter noun end in -a. This -a ending is attached to the BASE: Itinera sunt longa. (nom. pl.) . The journeys are long. Itinera longa facimus. (acc. pl.) . We are making long journeys.