There isn't any difference between somebody and someone, anybody and anyone, nobody and no-one.
1) Not + anybody / anyone, nobody / no-one are used for people in negative and interrogative sentences.
- There isn't anybody/anyone in the room.
- There is nobody/no-one in the room.
Not + anything, nothing are used for things.
- There isn't anything in the bag.
- There is nothing in the bag.
We can use nobody / no-one / nothing at the beginning of a sentence or alone only to answer a question.
- The house is empty. Nobody lives there.
- What did you say? Nothing.
- Who did you speak to? No-one.
The difference between somebody and anybody, something and anything, somewhere and anywhere, etc are the same as the difference between some and any.
2) Somebody / someone are used for indefinite quantity in the affirmative sentences.
- There is somebody/someone in the garden.
- There is somebody/someone at the door.
Somewhere, anywhere, nowhere are used for place.
- They live somewhere in the north of Ireland.
- Did you go anywhere interesting for your holiday?
- I don't like this town. There is nowhere to go.