N is the noun. ‘은/는’ is used with a noun to denote the topic or theme of a sentence. When the noun ends in a consonant, use ‘-은’, and when the noun ends in a vowel, use ‘-는’.

‘N이에요/예요’ is attached to the end of a noun to make the noun function like a verb in regular conversation. When the noun ends in a consonant, use ‘이에요’, and when the noun ends in a vowel, use ‘예요’.

저것은 볼펜이에요? Is that a pen?

우빈 씨는 누구예요? Who is Mr. Woobin?