when "I am" means "wo", it usually followed by adj. And if the word followed "I am" is none, it should be translated into "wo shi". For example, "I am a king" means "wo（我） shi（是） yige（一个） guowang（国王）". "I am very smart" means "wo （我）hen（很） congming（聪明）".

you can say "나는" or more politely "저는". "나는 왕이다." "저는 왕입니다" "나는 천재다." "저는 천재입니다"

I am a student。I am 20 years old。I am happy。 我是学生，我二十岁，我高兴。

这里很显然，是表达我是。

I am + noun = 我 是 = wǒ shì