Connect your USB storage device into the USB port at the back panel of your Linksys router.
NOTE : MAKE SURE IF YOU ARE CONNECTING A HARD DRIVE IT IS PLUGGED INTO THE POWER SUPPLY AS WELL.login into your linksys smart wifi page. Once in the page click USB Storage under Smart Wi-Fi Tools on the left panel. You should now see your USB storage drive in the Status tab.
To enable file sharing, you need to connect the external hard drive at the back of your Linksys router in the USB port.
Once it is connected you need to login to the router page.
Then go to the USB storage option on the left side of the panel
You can manage all the settings of file sharing from here