CoRE is a smartapp in smart things. You add it in the smarthingsIDE (shows logs, devices, apps and handlers, etc.) The link above should give you some points in the right direction.
I'll help you get into ide real quick.
Google smartthings ide. Should be first link.
Click the 3bars in top right and Log in to your smartthings account. Click the bars again and select location and then select your hub location( very IMPORTANT to make sure to do this step if it logs you out. If you don't select your hub location editibg to the ide won't reflect in your smartthings app. Made this mistake when I first got my setup.)
From there you will see tabs for your smartapps, handlers, devices, logs, etc. They will be located in the three bar tab or on the top of the page depending in your device.