Memories are used to remember states. Several of them could remember Binary values which can be very useful. The base to all memories is the RS NOR Latch. All memory circuits use it (except for Delay Line memory).
A Flip Flop takes the RS NOR Latch one step further. A Flip Flop is a circuit for an RS NOR Latch that gives the Flip Flop special functions.
The T Flip Flop
Also called a toggle, a T Flip Flop will change its output's state when the input turns on. It turns 2 input pulses into 1 output pulse. A T Flip Flop can be used to make binary counters.
T Flip Flops are commonly used to make buttons act like levers, as each press of the button would send an input pulse to a T Flip Flop, which would then switch the state of the T Flip Flop's output. An advantage to the combination of T Flip Flops and buttons is that you cannot tell when the output is on or off based on the button. Buttons are also used for aesthetics, but if looks don't matter, the lever is usually a better choice, as it is more compact.