The Accounts section of CSM provides information on the public cloud accounts you have already added. You can also add more account from this interface.
Each card represents an AWS account. You can see the summary on the card.
The colors for the circles mean the following:
Green: indicates the number of NSX-managed instances that are running without any errors.
Red: indicates the number of NSX-managed instances that have errors in them. If you click on the particular instance that has errors, you can see the error codes listed when you click on the red-colored arrow.
Grey: indicates the number of instances that are not managed by NSX.
Black: indicates the number of instances that are powered off.