You are correct.

You start with thorium plus a fissionable isotope of uranium or plutonium. The fission neutrons convert the thorium to U-233, which is fissionable. After that you rely on U-233 fission for neutrons and keep feeding thorium to it.

It can be done with solid fuel but with liquid fuel it works out really nicely. You can fission pretty much everything and have just fission products left over, which means a lot less nuclear waste that only has to be contained for a few hundred years. And you're not shipping anything fissionable to or from the reactor.