Automatic backup or rewrite?

I have used WD Essential My Book for a number of years, just updating with a new one.  I don’t think I’ve used it right in the past or to the maximum capibility…since I’m not the world’s most computer literate.

Will the Essential back up my files that I want back up automatically, or does it rewrite over existing files or create entirely new files from my computer?  In the past I have right clicked a file and did a “sent to”  the WD (my E drive).   Is that correct?    Is there anything I can do to save a whole “C” drive?   What else can I do?  

My computer recently crashed and though I had backed up some files a few weeks ago, it would have been nice if they were backed up automatically or on a schedule.   I would appreciate any help ;you can give me.  Thank you

If you want a complete backup of your computer, including Windows and Program Files, you can use Windows Backup, which comes as part of Windows, you can setup a schedule of when backups will occur.