D Flip Flop:

The D Flip Flop is a simple latch that takes in one input, and holds (latches) that as the output Q and it's complement Q'. Essentially a D Flip Flop is a SR Flip Flop with an inverter on one of the inputs to prevent the SR Flip Flop from going into an undefined state. D flip flops are less hassle than SR Flip Flops because you only have to deal with only one input, two states, and no undefined states.

It can be constructed out of an SR Flip Flop and an inverter on the appropriate input.

D Flip Flop State Table using 2-input Nor Gates :
D	Q	Q'	State
1	1	0	Set State

0	0	1	Reset State

D Flip Flop Diagram using a 2-input Nor Gate SR Flip Flop :

           |SR Flip Flop |
	   |             |
 D--X------|S 	         |-----------Q
    |      |  	         |
    |      |		 |
    ------O|R            |-----------Q'

Diagram Notes:
  Inputs: S, R	    
  Outputs: Q, Q'
  O= is an inverter
  X= The "X" is where one wire attaches to another wire