We use indefinite pronouns when we talk about people, things, or places in general, not about specific ones.
We say somebody, anybody, nobody, or everybody to talk about people.
We use something, anything, nothing, and everything to talk about things.
For places, we use somewhere, anywhere, nowhere, and everywhere.
We usually use some- in positive sentences, any- in questions and negatives, no- to give a negative meaning, and every- to talk about all people or things.
For example: Somebody is calling you. There isn’t anybody here. Everybody loves weekends.