D Type Flip Flop Behavior
A D Flip Flop will track its input 'D' in function of the clock.  'D' in this case stands for Data.  Note that as shown in the picture below, the output 'Q' is only toggled high or low depending on the clock signal.  Usually, a true value (1 or high) will trigger the input.  If D goes high and the clock is low, it will wait until the rising edge of the clock to trigger Q high.  So in general there are a few things to remember about a D Flip Flop:


The output Q and /Q are only triggered in function of the clock
It can be thought of as a memory cell
It is also named a bistable multivibrator
Memory units could have thousands/millions of flip flop tied together
A basic shift register can be made out of D Flip Flops




Finally, the picture below summarize essentially what I am trying to explain.  A Flip Flop is clock triggered, and the output will follow the input upon a clock trigger.  



Look into D Latch if you are looking at a Flip Flop that would be "level sensitive" and D Flip Flop if you want something that is "edge sensitive".  The output Q will only depend on the clock state and the input.