The FAQs should help. They both have step by step instructions.
The first one covers how to setup SmartThings to work with Echo. It sounds like you’ve already done that. But you may want to review the step on how to authorize additional devices as you add them over time.
NEW: Alexa IFTTT Triggers
As of November 12, 2015, there are now two official ways to integrate Alexa and SmartThings.
The first way is fast and simple, and can do any one thing that you can do in the official SmartThings IFTTT channel.
You pick any phrase you want to use, and use that as the “if” in the Alexa channel at IFTTT for a new recipe. Then you just pick from the dropdown options in the SmartThings IFTTT channel as the “that.”
To use a recipe, you say “Alexa, trigger {my phrase}.”
So you could say “Alexa, trigger open the pod bay doors” to open your garage door, “Alexa, trigger autodestruct” to turn on your siren, “Alexa, trigger kitchen lights” to turn on your kitchen light. Whatever you want. This is the power of IFTTT, and why SmartThings having a channel there is so u…
The second FAQ covers how to use echo for something other than just turn a single device off and on through SmartThings. So changing the mode, running a routine, etc.
On October 1, 2016, Amazon added the ability to turn on a " routine" from Alexa. If you want to use that method, see the official support article.
https://support.smartthings.com/hc/en-us/articles/210204906-Amazon-Alexa-SmartThings-Routines
Note that the official method will not allow you to use echo to run any routine that includes a lock or a Smart Home Monitor armed state change or another device class that Alexa does not know. The method described below in this FAQ will, but it does require that you create a virtual switch.
Although at present echo can only request that smartthings turn devices on, off or dim, by using a virtual switch, you can tell echo to turn that switch on or off, and then have all kinds of things happen in smartthings. For example, if you want to have echo tu…