After you enter your authentication details and these are accepted SME will discover any S3 compatible buckets that are available. You can choose which buckets you wish to add to your Account, and which will be the default bucket**. As part of this process you can choose to create a new default bucket if you wish, and also choose the reason.
Any buckets you choose not to index / sync will not be available to be worked with an you would need to go back to the Open S3 settings from the Dashboard to add them to your account. This is also the case with any new buckets you add directly from the S3 compatible provider.
** The default bucket is what is used for interactions with Smart folders