This is something that Korean language uniquely has.
We attach particles AFTER subject and object nouns to dintinguish what they are in the sentences.
However, in a collequial speach, they can be omitted.

Side note:
'c' means when the noun ends with a consonant.
'v' means when the noun ends with a vowel.

Subject Particles Obejct Particles
은(c), 는(v)   or   이(c), 가(v) 을(c), 를(v)

Subject Particles

How do we know which particles to use for subject if there are two types?
This is quite a tricky part.
It's not wrong to use one or the other, but it subtlely changes the meaning.

은, 는

There can be used for 2 situations;
one for general situations and the other for comparison.

1. General situations
저는 인영입니다. I am In-young.
저는 학교에 갑니다. I go to school.

2. Comparision
저는 피자를 좋아해요. 선생님은요? I like pizza. how about teacher?

Do you see the first particle; 는 after 저 is general situation and
the second particle; 은 after 선생님 is for comparison.

이, 가

These are used for emphasizing subject noun who does the action verbs.
I could use the same sentences above, but the meaning changes.

(저+가 becomes 제가)
제가 인영입니다. I am the one who is In-young.
제가 학교에 갑니다. I am the one who goes to school.
or you may just put an emphasis on I for 'I' am In-young or 'I' go to school when speaking in English.

Object Particles

을, 를

Object particles don't have any meanings like the subject particles
except they indicate the nouns with object particles are object nouns in sentences.