Over WiFi, most people use Astro File Explorer or ES File Explorer (both are free).  Once you have one of those, make sure both devices (PC and Phone) are connected to the same WiFi network.  Also, make sure any folders you want available to your phone are shared for network use on your PC.  After that, on your phone in whichever file explorer app you use...you should see your computer and be able to access the shared folders.  Copy/Paste/Delete/Create...whatever you wanna do....all from your phone.
				
			
	