The way WD Smartware backing up file is that it backup what you tell it to such Pictures, Documents, Movies and Other data to its proprietary structuring. To get the file back, you would need to use its Retrieve options. For example you want to retrieve a document file. You would need to go to Retrieve, Select file in its categories, then tell where you want to put them, to the original folder or desktop or any where you want it to.
If WD Smartware is too complex for you.
You can try this suggestion below.
You could manually create a folder on the WD external drive name Back Up.
Under Backup folder you can create subfolder name My Doc, My Pictures, My Movies and so on.
Then you would just copy files from your internal drive to those folders you created on the external drive.
When you need a document file, just go to the My Doc folder. Is that simple?