I studied some QM on my own a while ago and while I could just do what the problems asked me to, I was really confused about how a quantum system is supposed to

I studied some QM on my own a while ago and while I could just do what the problems asked me to, I was really confused about how a quantum system is supposed to evolve assuming the state collapses. Then I got to density matrices and understood what that "parallel universes" thing actually is... It removed a major source of confusion.