SUBJECT

The subject is the agent og the sentence in the active voice; it is the person or thing that performs or is responsible for the action of the sentence, and it normally precedes the verb. NOTE: Every sentence in English must have a subject. (In the case of comands, the subject [you] is understood.) The subject may be a single noun.

Coffee is delicious.
Milk contains calcium.

The subject may be a noun phrase. A noun phrase is a group of words ending with a noun. (It CANNOT begin with a preposition.)

The book is on the table.
The new red car is John's.

Examples of subjects:

We girls are not going to that movie.
Goerge likes boats.
Mary, John, George, and I went to a restaurant last night.
The weather was very good yesterday.
The chemistry professor canceled class today.
The blank closed at two o'clock.

It can act as a pronoun for a noun or can be the subject of an impersonal verb. As the subject of an impersonal verb, the pronoun is not actually used in place of a noun, but is part of an idiomatic expression.

It rains quite often here in the summer.
It is hard to believe that he is cry.