If all you want to do is backup an external drive and the contents are stable and don't change then all you need to do is to copy all the files from one external drive to another external drive using copy and paste method.
If the contents are frequently changing then to keep your backup up to date you would then only need to copy the new or changed files, in this situation you don’t want to clone the drive you need a backup solution - the two are different. Cloning creates a duplicate of the drive onto another drive, while this is a form of a backup, to clone a whole drive is time consuming and inflexible it only creates a snapshot image at one point in time. For a fresh backup you have to repeat the process. As the backup drive is a complete copy it cannot be used for anything else
A Backup solution such as acronis or macrium is different. This can be set to backup the contents of your computer or a single drive onto another external drive as a backup file. The initial backup does indeed backup all the contents. Subsequent or incremental backups need only to copy new or changed files, in this way subsequent backups are smaller and quicker, it also makes it possible to retrieve earlier versions of files impossible by cloning.
Also there is no need to duplicate post in other sections, this just creates unecessary work for answerers if the questions has already been answered elsewhere