You probably already know this, but just in case, a “device type” is the same thing as a “device handler.” Smartthings has changed the terminology from time to time, so you will see both terms used in the docs and the forums.
Smartthings code uses a groovy variant.
Have you had a chance to look at the developer docs yet? Go to the first page of the forums by using the community link at the top right. Then go to the developer docs via the link at the top right of that page. They have examples There. If you have any questions, you can come back and ask in this part of the forum.
And if you have any questions about how to “publish” a device handler to your account after you modified it, this FAQ should help:
