What is an instance?

An SFTPCloud instance is the equivalent of an SFTP/FTPS server, managed by SFTPCloud. Because it's already managed, you don't have to worry about scaling, updates, and other maintenance tasks.
Besides being a worry-free SFTP/FTPS server, it is also cloud-native. This means that the data is stored in the cloud and you can access it by using other protocols besides SFTP/FTPS such as S3, GCS, Azure Blob, etc.