I was wondering what the difference between backing up folders/files using drag and drop vs. syncing vs. using backup software to back them up. Does it make a difference? I would guess that using backup software to save files/folders you would need to use the software to recover or view the files/folders? What method takes up the least amount of space on the external drive?
If recovery is needed which backup method makes recovery easiest?
What advantage if any is it to use syncing vs. using incremental backups?

If doing incremental backups do I need to save the previous incremental backup? I have read that keeping previous incrementals back ups is need and also have read that the previous incremental back up does not need to be saved.

Please make your answers simple to understand.
Thanks.

Just copying files uses the most space. Using a backup utility saves the most space. It can also schedule backups to be sure they are done regularly. Whether you save incrementals depends on whether you need to recover previous versions. Syncing just makes sure your backup is the same as your current hard drive.