Can I backup the whole computer?
Yes you can, but MultiCloudBackup is not designed for this usage. Backup only files that are really important to you such as your Documents folder.
How to launch MultiCloudBackup at startup on Mac OS X?
How to restore my files after a fresh installation of my OS?
First you need to download and install MultiCloudBackup. Then, at the setup stage, choose the restore config option. MultiCloudBackup will connect to one of your storage to restore its configuration. When it's done you can restore your files.