The thing about Lynch is that he steadfastly refuses to explain his movies. He expects the viewer to craft their own unique experience from the films. That being said, there are a lot of good "interpretations" of these two film out there. Just remember that all theories are "unofficial". They don't give anda enough luar angkasa here in the Answer section to fully answer your questions, but here are a couple of links:
This is probably the best take on "Mulholland Drive" I've seen, and most Lynch fan pretty much agree with it's conclusions:
link "Lost Highway" is a slipperier fish, so there are a few takes on it, but here are a couple of pages I've found useful:
link link Finally, anda can find a lot of knowledgeable Lynch fan here:
link Read through the forum if anda visit that last link. If anda have questions, chances are someone's already started a topic on it.