The Nominative case endings for the singular forms of the nouns in the first three declension classes are: -a, -o, and no vowel (zero). The Nominative ending of an a-declension noun is spelled -a if the stem ends in a plain consonant (e.g. Вљра) and it is spelled -я if the stem ends in a palatalized consonant (e.g. Ђня). The fourth declension class nouns all end in -ь in the Nomoinative case.
The subject of a sentence is normally in the Nominative case, just as in English. That is the principal function of the Nominative case. Sentences which have the verb is in English, like 'It is he. He is here.' use the Nominative case in Russian (not as in colloquial English: 'It's him'). In the following examples the Nominative case forms are in italics:
Рџчка слљва. The pen is on the left.
Јто рџчка. That's a pen.
Јто ћн. That is he. (Colloquial: That's him.)
Гдљ стакђн? Where's the glass?