Sentence Structure
Korean sentences follow the below structure:

SUBJECT (S) + OBJECT (O) + VERB (V)

Example:
I ate an orange.
    나는    오렌지를   먹었어요
(naneun orenjireul meogeosseoyo)
  The Korean word 이다 (i-da) means “to be” which serves like an English “be”-verb in a subject + noun sentence. 

Example:
I am a student.
     나는   학생  이다 
(Naneun haksang ida)

With the same meaning, this sentence can be changed into: 
     저는    학생 입니다 
(Jeoneun haksang imnida) → I am a student 

Comparing the two sentences, “저” (Jeo) is more formal than 나 (Na) and -ㅂ입니다  is the formal and polite ending of “이다” . 

SUBJECT + VERB

The base form of the verb “to go” is 가다. This sentence also means “I’m going.”
In Korean, by simply altering the endings you attach to your verbs, you can easily make many different kinds of sentences.

Few common verbs in Korean:  

하다  (hada)	To do
가다  (gada)	To go
보다  (boda)	To see
먹다  (meogda)	To eat
자다  (jada)	To sleep
돕다  (dobda)	To help

SUBJECT + ADJECTIVE
Adjectives in Korean can function like verbs if they are conjugated into present and past tenses. However, when describing nouns using adjectives placed in front of them, like “a beautiful picture”, the adjectives must be conjugated to a descriptive form.

Thus, we don’t use “이다” when describing a subject in a subject + adjective sentence in Korean. 

Example: I’m tired.
   나는   피곤해요
(naneun pigohaeyo)

KOREAN QUESTION SENTENCE
Korean language formulates a yes-no question simply by changing the sentence ending, from -ㅂ/습니다 in statements into -ㅂ/습니까 as questions. All other elements in the sentence remain in their places. 
-ㅂ니까 is added to end-vowel stems, and 습니까 is added after end-consonant stems.

Example:
       Are you a student? 
     당신은  학생  입니까? 
(Dangsineun hakssaeng imnikka?)