It's a hex d-type CMOS flip-flop (6 flip-flops in one package). A flip-flop is a bistable, one-bit memory storage circuit that's useful in building certain types of logic circuits.
A simple example would be to use one with a push-button to flip it on and off and control a light. Thus the light would be turned on and off with a push-button.
Yes. The FF output follows the D-input value after it is clocked. It retains that data value until the next clock pulse after the D value changes.
There are also J-K flip-flops with two inputs. A high on the J input sets the FF output high after a clock pulse. A high on the K input sets the FF output low after a clock pulse. A low input on either the J or K input has no effect on the FF state. If both the J and K inputs are high then the FF will alternate its state after each clock pulse.