It is right if we use någon instead of något?
No, någon can mean 'some'/'any' together with a word: Har du någon mat? 'Do you have any food?', but on its own means 'someone'.
This explains everything, thank you so much :D
why is "behöver du att köpa någonting" wrong?
behöva is a modal verb and doesn't take the att.
Why is using ingenting wrong here please?
Ingenting means nothing! Asking "do you need to buy nothing" doesnt make sense (:
Can I say "någonting"?
Yes, I need to buy a plane ticket to Sweden. Tack!