To add weather tile, use the SmartThings IDE Web Page > My Devices > New Device, add SmartWeather Tile. It will be listed as one of your Things that you can Authorize (in My Locations), and then it is available in Thing inventory to add to Panels.
When you create it, use any unique random value for "Device Network ID", for example, "SWT01".
If you're have trouble with the SmartThings IDE Web Page, check out this link for a little help:
Customer support service by UserEcho