How should I connect my light fixture?
For the switch turned off to short things, it must be a 3 or 4 way switch. The 2 white and 2 black could be travelers, the most likely connection then is lamp black to switched power red, lamp white to the 3 white, probably neutral. It's worth buying a non-contact circuit tester, they aren't all that expensive and can be a literal life saver. You can then quickly locate the proper switched power and deduce which is the neutral, because my guess at what to connect is only a guess. The circuit tester will tell you for sure.