To create a new backup, you must first have added a company and enabled backup for it. Then, go to the Backup page and select "New Manual Backup". You can then select from "Incremental" (look for changes since the last backup), "Full" (look for changes in all objects), or "Complete" (completely refresh all objects ChronoBooks has backed up).
Manual backups are not necessary, as ChronoBooks continuously backs up your data. If you're about to undertake a big project or import, you may want to make a manual backup.