Q. How are something and anything used?
A. Basically the same way some and any are used.

something is used in positive sentences:
  It appears that something large made this dent.

anything can be used in positive sentences when used as it doesn’t matter which:
   You can get just about anything at a flea market.

anything is used in positive sentences following never, hardly or without:
   It seems there is never anything to eat in this house.
   There is hardly anything to see when driving across some states.
   The bull made it through the china shop without anything breaking.

anything is used in negative sentences:
   There isn’t anything interesting on TV tonight.

anything can be used in a positive sentence when the sense of it is negative:
   I decided not to loan them anything from our equipment locker.

anything is used in questions:
   Does anything else seem to matter when you don’t feel well?

something is used in questions where we hope the answer is “yes”:
   Can something in this medicine cabinet give me relief from this headache?

something is used in questions when offering or requesting:
   Could I please have something to read while I wait?