Translation:Please put a stamp here.
Yes, stick works well for stamps. You can also use haru for "sticking" something to the fridge with a magnet for instance - I'm trying to think of the right word for that because sticking something to the fridge sounds a little odd but I can't think of it. Maybe I'm just being paranoid.
きってstamp ここhere はって to enter usually a structure but I guess like in english to enter information. ください please do Might be easier for beginners to have something like stamp in katakana or kanji with yomigana so you know it isn't the verb "to come". Anyway if it was going to say come here it would be location then verb invariably. ここにきってはってください。 might confuse people who are just learning sounds like "please come and enter here". But whatever duolingo can do whatever it wants.
はって does NOT mean enter. It means to stick or affix something, ie. in this instance the stamp きって. Please read the other comments on a thread before commenting yourself. Also it doesn't make sense in English OR Japanese to say "please enter the stamp here", even without kanji きって the noun meaning stamp and きて a form of the verb くる to come are spelt differently, きって is followed by をindicating that it is the direct object of the verb - NOT a noun and Japanese word order, logic and context all make it clear what the Japanese is saying and clear up any potential confusion with homonyms! And I think you mean ふりがな.