The C-MOS IC 4013 contains two edge-triggered D flip-flops.
With the circuit shown, you get to know an edge-triggered D flip-flop. You use not a proper clock signal, however a pushbutton switch (Clk) can illustrate the principle just as well.
With the push button D, you control the D input of flip-flops. The flip-flop switches at the precise moment in which you push the push button Clk. The Clk signal jumps from 0 to 1 at the rising edge. In all other situations, the flip-flop remains closed.
Besides the D flip-flop, there are more classes of flip-flops...