The Generic Mirrored Backup script template is for backups that don't have a template more specific to a particular task or situation. Settings are simply preconfigured to reasonable defaults.
This script template may be chosen when you create a new script.
Synk at the very least needs to know which folders you're backing up from and to. This is configured in the Locations area of the settings.
Need more guidance? See Specifying Locations.
At this point, you're generally in good shape! Synk uses sensible defaults, so the remaining settings are probably already what you want. Try turning on the script to begin the mirroring. If you want to approve Synk's actions before it takes them, to make sure you have it configured the way you want, you can use the Preview Proposed Actions setting.
Many other settings are available if you want to further customize the way the script works. See Script Settings.