Someone, somebody, something, somewhere are indefinite pronouns. They function in a similar way to some. We use them in affirmative clauses and in questions expecting a particular answer. We can use them to refer to both general and specific people or things. We use them with a singular verb:
I know someone who gives piano lessons. (a specific person)
Somebody has obviously made a mistake. (general, we don’t know who)
Can you hear something?
There was no mistaking the smell. Burning. There was a fire somewhere.
We often use the plural pronoun they to refer back to (singular) someone or somebody when we do not know if the person is male or female:
Never judge someone by the way they look. (or Never judgesomeoneby the wayhe or shelooks.)