SyncToy is a free application from Microsoft. It can be very useful for keeping two folders identical between user accounts, across network drives, or for backup purposes. It does not have as many features as a full, commercial backup application, but it can be useful for light-duty backup and sync. 

Download and Install

You can get the latest version of SyncToy from this page:
The installation is pretty straightforward, and you will be asked whether or not to submit usage statistics to Microsoft.

Set Up Sync

Once you have the program installed, run it, and you will be greeted with a welcome screen. Click “Create New Folder Pair” to get started.

Next, you will need to select a “Left” folder and a “Right” folder. You can think of the left folder as your main folder and the right folder as your backup folder.
  Next, you will need to choose what kind of synchronization you want. There are three options here: 
  • Synchronize
    (files are synced in both directions including renames and deletes)
  • Echo
    (files are copied left to right and so are renames and deletes)
  •  Contribute
    (files are copied left to right and so are renames, no deletes)
Note: If you are not sure what to choose, don’t worry, you can change this later.
Next, choose a name for your folder pair and click “Finish”

Customize & Run Your Sync

After your folder pair is set up, you have the following options for customizing and running your sync: 
  1.  Change action
    (switch between synchronize, echo, and contribute)
  2. Change options
    (include/exclude specific files)
  3. Preview
    (perform a mock sync to test for potential issues)
  4. Run
    (run the actual sync)

SyncToy can also be run from the command line or set up as a “Scheduled Task”. There is a great tutorial showing how to do this at the How-To Geek website: