RFID is the same basic technology that you use in your car to listen to the radio. A radio tower sends out radio waves that your car antenna picks up even through obstacles like trees.
RFID does this on a smaller scale. A device is used to send out the radio waves which are picked up by the small RFID chips. The chips antennas then shoot that wave back with their unique identification. Hence the ID in RFID.
This means that you could have a pile of boxes full of clothes and without opening the boxes you just scan the area with the RFID reader and all of the items would show up on the simple RFID app on your phone.