Did you get a chance to read the FAQ at the link I just gave you?
What you are going to do is create a virtual device which is both a switch and a sensor.
So it will look like a sensor to echo, and that is what will trigger the echo routine.
But it will look like a switch to SmartThings so you can turn it on and off. You do not need webcore for this, although you can do it that way if you want to.
So when you turn on the “switch“ with any smartthings routine or automation, it will look to echo like the “contact sensor” just opened. And when you turn the “switch“ off with any smartthings routine or automation, it will look to echo like the “contact sensor” just closed. So this is a very easy way to trigger echo routines from smartthings.
The FAQ has all the instructions when you follow its links. So just use those. This is a very popular integration and many people in the community are using it.
Here is the FAQ link again. ( also note that echo routines can be triggered from either a motion sensor or a contact sensor. But not a switch, as you noted.)
FAQ: Can I trigger an Echo Action without Speaking to It?