Grammar Pulis

You asked:
When do you use "somebody" and "someone"? How about "everybody" and "everyone"?

Grammar Pulis answered:
To make sure I give you the right answer, I consulted 3 sources:

Elements of Style by William Strunk and E.B.White
Usage & Abusage by Eric Partridge for Penguin Reference Books
Merriam Webster's Collegiate Dictionary

All of them agree that:
somebody is synonymous with someone;
everybody, with everyone;
anybody, with anyone;
and nobody, with no one.

Somebody and someone both mean "some person of unspecified or indefinite identity."
Everybody and everyone both mean "every person."
Anybody and anyone mean "any person."
Nobody and no one mean "no person."

Take note that except for no one, all are spelled as one word. There are instances when you have to spell these in two words: some body, every body, any body, no body. That is when the word body means a corpse, a human form, or a group.

Let's try out some sentences:

Somebody/ someone/some person has to bring a body to class.
Some body will be used for the anatomy class.

Everybody/ everyone/ every person will eventually die.
Every body in the morgue has been embalmed.

Anybody/ any one/ any person can replace our bikini ad model.
Any body of water would do for the beach scene backdrop.

Nobody/ no one/ no person claimed the confiscated car.
No body was found in the trunk.

Somebody may also mean "a person of position or importance" as in:
He thinks he is a somebody just because he's been promoted.
Nobody means "a person of no influence or consequence" as in:
She only dates nobodies to have a sense of superiority over her men.

I hope this was helpful to you. Keep on asking your questions, and I will do my best to answer.