Lets consider a 1D (e.g. Audio) example to see what the different domains mean:
Consider a complicated sound such as the noise of a car horn. We can describe this sound in two related ways:
In the example below (Fig ) we have a signal that consists of a sinusoidal wave at 8 Hz. 8Hz means that wave is completing 8 cycles in 1 second and is the frequency of that wave. From the frequency domain we can see that the composition of our signal is one wave (one peak) occurring with a frequency of 8Hz with a magnitude/fraction of 1.0 i.e. it is the whole signal.
Relationship between Time and Frequency Domain