its usually the first word, but not always. it's the person or object that does the action, or that is being described.
The subject is the part that goes before the verb (in statements).
eg
Jack lives here.
My brother and his wife are arriving today.
We played cards all night.
The subject usually begins a sentence.
The subject is normally a noun phrase or pronoun.
The subject normally describes the 'doer' of an action.
The verb and the subject agree ie singular or plural (first example = singular)
The subject of the sentence is "you"
To locate the subject in the sentence you ask, who or what is doing the action in the sentence.
You is the subject of that sentence.
"They" is the subject of that sentence.
The subject isn't shown but the subject in that sentence is "you".
A subject in a sentence is who, what, or where the sentence is about.
The subject is who or what the sentence is about.
A subject is what the sentence is about.To make a sentence with a subject think like if it was a theme.
The subject of the sentence is "you"
What is the subject of this sentence? She was the subject of an investigation.
The subject tells who or what the sentence is about.
Does a sentence need a subject?
Who or what the sentence is about is the subject of the sentence.
Who or what the sentence is about is the subject of the sentence.
The subject of a sentence is who or what that sentence is about.
A sentence missing a subject or a verb is a fragment.
That would be the subject of the sentence.