Something refers to a specific person, thing or place, while anything can refer to any person, thing or place without being specific. Nothing is used with a negative verb to indicate that nothing was done or nothing exists, and it is incorrect to say "I didn't do nothing." Anything and nothing are also used in short answers or sentences with a positive verb but a negative meaning.

1. Something, anything, nothing
EF pre-intermediate 4C

2. With a positive verb when you don’t say
exactly who (person), what (thing) or
where (place)
In questions or with a negative verb
I didn’t do anything last night
NOT: I didn’t do nothing
In short answers or in sentences with a
positive verb (the meaning is negative)