You are saying about 저는(jeoneun) which can be pronounced as 'chonun' by English speakers.
And let me explain about it.
저(jeo) is a humble form of 나(na) which means "I" in english.
는(neun) is one of subject marking particle.
So, 저는(jeoneun) means "i __" or "I am __" in a sentence.
It can be omitted in daily conversations though,
the sentence would be more clearer when you put that in.
A: 이름이 뭐예요? (ireumi mwoyeyo? : What's your name?)
B: 알렉스입니다. (alex imnida : I'm Alex)
A: 누구세요? (nuguseyo? : Who are you?)
B: 저는 알렉스입니다. (jeoneun alex imnida : I am alex)
As you see, it is used when you emphasis a word or thing.
You : 너(neo)
Me : 나(na)
But you can't use the word "너" for everyone.
It's only for your friends or someone is much younger than you.
Then how about a stranger or someone you're supposed to be polite to?
There is a word 당신(dangsin) but this sounds less polite in colloquial either.
Because Korean people tend to avoid addressing "you" directly because it might be kinda rude.
The best way for addressing a stranger would be calling their titles such as
아저씨(ajeossi : older male looks married)
아주머니(ajumeoni : older female looks married and having grown up children) *warning: some ladies hate to be heard as this
학생(haksaeng : someone looks younger than you and be like a student)
그쪽 분(geujjok bun : around your age and you have no idea what his/her title is)
Hope this helps! ;-)