The spread spectrum concept, like all great innovations, is at its core very simple. First, you take an information signal and code it so that it looks more like noise. The spread spectrum transformation, in effect, protects the information while it is in the medium. The latest techniques seem to offer good protection if applied to a well-designed system. Remember that the goal is to make an information signal look more like noise.
Noise is completely random.
So, this coding transformation also spreads out the information signal to make it less descernible. The easier concept to grasp is FH, in which the information simply hops from one frequency to another. If one frequency is jammed by noise or interference, the information still gets through using the other frequencies. Similarly, because the FH transmitter is hopping from one frequency to another, it is only likely to cause interference during the portion of the time that it spends on the frequency that is being used for other traffic. Frequency hopping works well for lower data rates because it can hop over several frequencies during each bit of information.