How I can link Arduino Mega to Amazon Echo?

It doesn't matter wether or not it needs to be via wifi, bluetooth or internet. I just wan't to find a solution becasuse there isn't an explanation to this problem, I could only find examples but in those it didn't explain how the person did it.

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ieee488:
Control Your Amazon Echo Remotely With Your Phone

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Yeah but how can I send commands to arduino with alexa so when I say for example turn led on a led connected to arduino turns on. Not how to connect with alexa by a phone.