Translation:Du trenger intet frimerke for å sende et postkort.
Jo, det gjør du!
What's the difference between intet and ingen?
"intet" is the neuter form of "ingen."
This sounds archaic. I would rather say "Du trenger ingen frimerker".
Why is is the "for" here in this sentence?, why isnt å sende enough?
"For å" has the meaning of "in order to." Without the "for," this sentence makes no sense in Norwegian.