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A flip-flop is a bistable device. This means that if you put it in one state it remains there on its own until you overtly set it to the other state. This is one way of making a memory element. It is not the method used in your dynamic RAM, since it can't be made at those high densities. Dynamic RAM is more akin to a capacitor that holds the charge you put on it. Since this charge is going to leak off, the states have to be periodically refreshed. This is why it's called Dynamic RAM, as opposed to Static RAM.
In simple implementations, one can take two devices and feed the output of each back to the input of the other. The output of each is also controlled by a separate input. If the output of one device is a logical zero, and a logical zero causes the second device to assume a logical one, then the zero from the first will set the second to a one, the one, which is fed to the first device, will cause no change, so the ouputs will be stable. If the second input to the first device is set to zero, it will force the output to a one, which will, in combination with the second input to the second device, flip the second device's state. This state will latch the state in the first device, so that the new, opposite, state is preserved until new overt actions is taken at the input.
In a synchronous device, these controlling inputs are not applied to the elements until a separate clock signal is applied. This clock may act according to its level, which is generally called "gating", or it may act only on the positive or negative edge of its signal. This is typically called "clocking."
Obviously, this is not a thorough treatise on the subject of either flip-flops, or memory. Your useless item of information for the day is that the term, core, which is widely used to refer to memory, comes from an old technique which used ferrous, toroidal cores to hold the state of the memory element. The magnetic field, which was set to a particular direction by the direction of current in the windings, would remain there until the windings were driven in the other direction. This kind of memory is non-volatile, which means it retains its state even when power is off. The last time I used it, about 40 square inches would hold 256 K. Yes, that's a K, not an M or a G.
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