best option: https://community.smartthings.com/t/smartthings-api-browser-now-available-to-all/249907
to view your devices online: https://my.smartthings.com
to manage from your desktop: CLI
the legacy IDE: https://graph.api.smartthings.com/ go to My Locations and tap on your Location name
BUT… THIS IS LEGACY AND NOT MUCH YOU CAN DO THERE. IT WILL BE SHUTDOWN SOON!