Getting basics to work (denon, myopenhab, Alexa)

Setup, Configuration and Use Beginners
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You need to tag your item according to:

Switch KitchenLights "Kitchen Lights" <light> (gKitchen) [ "Lighting" ]

so the [ "Lighting" ] does the magic for Alexa. Another option is [ "Switchable" ]

You don’t need to expose any items, setting up a working openhab cloud is sufficient. AND you need to give the Alexa skill access to that cloud.

So basically reading the post in the link above should answer all your questions.