SOMEONE / SOMEBODY. They are used mainly in affirmative sentences:

There is someone at the door. 

ANYONE / ANYBODY. They are used when the sentence is interrogative or negative:

Is there anyone at the door? No, there isn't anyone at the door.

NO ONE / NOBODY. They are used in negative sentences but the verb must not be in the negative form:

There is nobody in the park because it is very late.

When you want to refer to an object, action, activity, idea, etc. without saying exactly what you mean:

SOMETHING is used mainly in affirmative sentences: 

He is hiding something in his hand.

ANYTHING is used when the sentence is interrogative or negative:

They didn´t do anything interesting on Saturday.

NOTHING is used in negative sentences but the verb must not be in the negative form:

There is nothing in the fridge.

  SOME / ANY can be used to refer to a plural noun or uncountable noun already mentioned.

SOME is used mainly in affirmative sentences:

There are some boats on the water and some on the sand.

ANY is used mainly in interrogative and negative sentences: 

My sister has a lot of money but I haven't any.