(used to represent an inanimate thing understood, previously mentioned, about to be mentioned, or present in the immediate context)

It has whitewall tires and red upholstery. You can't tell a book by its cover.

(used to represent a person or animal understood, previously mentioned, or about to be mentioned whose gender is unknown or disregarded)

It was the largest ever caught off the Florida coast. Who was it? It was John. The horse had its saddle on.

(used to represent a group understood or previously mentioned)

The judge told the jury it must decide two issues.

(used to represent a concept or abstract idea understood or previously stated)

It all started with Adam and Eve. He has been taught to believe it all his life.

(used to represent an action or activity understood, previously mentioned, or about to be mentioned)

Since you don't like it, you don't have to go skiing.

(used as the impersonal subject of the verb to be, esp. to refer to time, distance, or the weather)

It is six o'clock. It is five miles to town. It was foggy.

(used in statements expressing an action, condition, fact, circumstance, or situation without reference to an agent)

If it weren't for Edna, I wouldn't go.

(used in referring to something as the origin or cause of pain, pleasure, etc.)

Where does it hurt? It looks bad for the candidate.

(used in referring to a source not specifically named or described)

It is said that love is blind.

(used in referring to the general state of affairs; circumstances, fate, or life in general)

How's it going with you?

(used as an anticipatory subject or object to make a sentence more eloquent or suspenseful or to shift emphasis)

It is necessary that you do your duty. It was a gun that he was carrying.

Informal . (used instead of the pronoun its before a gerund)

It having rained for only one hour didn't help the crops.

(in children's games) the player called upon to perform some task, as, in tag, the one who must catch the other players.

Slang .

sex appeal.

sexual intercourse. ?

get with it

Slang . to become active or interested

He was warned to get with it or resign.

have it

Informal .

to love someone

She really has it bad for him.

to possess the requisite abilities for something; be talented, adept, or proficient

In this business youeither have it or you don't.

with it

Slang .

aware of the latest fads, fashions, etc.; up-to-date.

attentive or alert

I'm just not with it early in the morning.

understanding or appreciative of something, as jazz.

Carnival Slang . being a member of the carnival.