Firstly, if you are not already aware, whenever you see instructions to login to the IDE at graph.api.smartthings.com you should use https://account.smartthings.com/ instead. If you get redirected to graph.api.smartthings.com that’s fine, but you may get redirected to another ‘shard’ instead and that is where you want to be. You don’t want to install stuff on NA01 (graph.api.smartthings.com) when your account works with e.g. NA04. You can do it but it won’t achieve anything.
WebCoRE is a collection of four SmartApps. If you have only been working with ‘Device Handlers’, all you have done is install a device driver for the webCoRE mobile app which can act as a presence sensor.
https://wiki.webcore.co/ is the closest there is to ‘official’ install instructions.
Once you’ve done the IDE side of things, you can load the app into your location using the new app. Just hit ‘+’ on your app dashboard, choose SmartApps, and webCoRE should be listed under ‘My Apps’ at the bottom of the page. It works though it might look slightly different to it does in the Classic app - the retrofit of Groovy SmartApp settings to the new app is slightly quirky for some apps.
Oh, and you’ll find a dedicated community forum at community.webcore.co who will help you out.