With frequency hopping only one frequency is used at once, and they're selected according to a sequence that matches a shared PRNG. As I understand it, that's what Bluetooth and some Wifi links do. They switch between discrete bands very fast.
Spread spectrum is a little different. During modulation, as with FM a series of side bands spread out. Normally we would limit these as they're considered "interference". But with the right modulator you can spread (and indeed encrypt at the RF link level) information into some bands but not others. Although all sidebands are present, to an observer who can't tell which ones carry the data at any moment, it makes no sense to even try demodulating the signal.
Neither solutions are much use if you need to communicate back because triangulation alone is enough to find you.
Curious if this tallys with your understanding, its over a decade since I had anything to so with this sort of thing. The best summary I recall was in Ross Anderson's "Security Engineering" book (first ed.)