When a noun is in the accusative case, it means that this noun is a direct object. In other words, we do something to this object directly: we give it, we take it, we see it, we kick it, etc.

Let's recall some around the house words and see how they transform into the accusative case:

tušinukas (a pen) becomes tušinuką
sąsiuvinis (an exercise-book) becomes sąsiuvinį
televizorius (a TV) becomes televizorių
knyga (a book) becomes knygą
kėdė (a chair) becomes kėdę
kambarys becomes kambarį

Notice that the singular endings are ą, ę, į and ų (nasal vowels).

Now let's make their plural forms into accusative plural:

tušinukai (pens) becomes tušinukus
sąsiuviniai (exercise-books) becomes sąsiuvinius
televizoriai (TVs) becomes televizorius
knygos (books) becomes knygas
kėdės (chairs) becomes kėdes
kambariai becomes kambarius

Notice that the plural endings always end in s.