I think I understand "changing keys" a little better now. Basically you play a chord that "means" one thing in the previous key, but means something else in the new key, so the listener follows the chord thinking it belongs to the previous key but surprise! it leads them somewhere else. If you'll forgive me the crude approximation, it's a little bit like a "your mom" joke, in that the same words suddenly get a whole new context. Am I making any sense? I'm sure there's a lot more to it, so if you've got any wise words I'm listening. Thanks!
that is one way to change keys. but sometimes you can also do it with no pivot