Lets start here.
Things and items are different. Graphical source
Things can be defined in both PaperUI and Textual. You can use things( the items linked to the channel ) created via PaperUI and textual configuration both in rules.
Both should be available for rules.
You do note define devices, you define things by adding them from the Inbox.
Things can have Channels, each channel is for a special purpose.
- Light On / Off Switch
- Color temperature
Each channel needs one Item so you can control the channel.
Channels can be linked to more then 1 Item.
Checkout the Concepts
Each channel you see is linked to one Item.
You can use the items linked to the channel with your rules.
Also this Matrix is very useful
Do you know Node-Red? Its a graphical rule engine.