The current version is 2.2.4a and was released Friday. It is rather stable and the main thread for that version is here: [DEPRECATED] Ask Alexa 2.2.4
Thinking of it as a THREE part setup is probably more accurate:
First set up the app within SmartThings. Configure it, the get your setup variables
Set up you AWS Lambda Code
Set up the Developer Area with the variables from the first step.
I am here, along with over a thousand others that have installed this, ready to help.
The documents are in the order you should proceed, and if you follow them exactly it SHOULD work 
http://thingsthataresmart.wiki/index.php?title=Ask_Alexa
If you run into ANY issues, I recommend going to the 2.2.4 thread above and you will get some help.
Good luck!