A few nouns in Lithuanian are used only in their plural number. They are called plural nouns. Even though they indicate one object, you need to use the plural endings:

durys (door) - not "duris"
grindys (floor) - not "grindis"
marškiniai (a shirt) - not "marškinys"
miltai (flour) - not "miltas"

It is the same as the English word scissors, which in English and in Lithuanian is a plural noun: žirklės.

A plural noun that you are going to come across every day is metai, meaning a year. You must only use its plural endings:

metai
metų
metams
metus
metais
metuose
metai!

Although metas in singular means a time:

Metas eiti namo. It is time to go home.
Dabar negeras metas skambinti draugams. Now is not a good time to call the friends.

Kokie gražūs metai! What a nice year!
Kokiais metais jūs gyvenote Lietuvoje? In what year did you live in Lithuania?
Skambinkite į duris! Ring the door!
Jie perka gerus miltus. They buy good flour.
Mums nepatinka šios medinės grindys. We don't like this wooden floor.
Paduok šitas žirkles. Pass me these scissors.