Concepts

• Utterances are how the user would speak to Alexa. It's a list of things that the developer would define that would encompass all the phrases that someone can use to trigger your app.
• Intents are how Alexa handles the requests that the user makes to Alexa. There are 3 required intents that Alexa forces you to have: AMAZON.StopIntent, AMAZON.HelpIntent, and AMAZON.CancelIntent. These are fairly self explanatory.
• Slots are basically the variables that you'd want your user to fill in when making an utterance.

Architecture of an Alexa Skill

Here's a simple sequence diagram of what happens when a user asks Alexa something.

Lambda is a really useful tool that Amazon Web Services has built to allow you to run a service without provisioning your own servers. In an Alexa Skills context, it's what the Alexa service calls when a user calls your skill. This is where the code for your skill lives.