Indefinite pronouns (= неодређене заменице) are called such because we don't always know who or what we are referring to.
Bear in mind the following things:
We use some and its compounds (- one, body, thing) in:
positive statements (They bought some honey.)
questions expecting a 'yes' answer (Do you want to hear something?)
offers and requests (Would you like some juice?)
We use any and its compounds (- one, body, thing) in:
negative statements (We haven't got any fruit.)
questions (Do you want anything from the market?)
with hardly, barely, scarcely (I have hardly any time.)
We use a singular verb with everybody / everyone / everything (Everyone's ready.)
We use plural forms they / their with all compounds (No one saw Tom go out, did they?), except those with -thing (Something went wrong, didn't it?).
Try the quiz here.