
Yeah, I just had a midterm on that stuff last week. Quantum is pretty interesting stuff.
If you didn't quite understand that last bit about "collapsing the wave function", in QM (Quantum Mechanics), you are always talking about the wave function, which describes the probability of finding a particle at a particular location and time (systems change over time). Notice, that this is a
probability - not a guarantee as to what will happen. The probability is determined by what the system started out with (a measurement at some point in time) and the time that has passed.
(Think of the fact that if you roll a die 6 times you "should" expect to see one of the numbers once each - but that doesn't always happen)
When you go and take a measurement, you collapse the wave function, since you know that the particle was "here" and "now", with a probability of 100%. This changes the way that the particle will behave from that point on.
The fact that the parrticle seems to go through both slits is due to a concept called the particle-wave duality, where we can actually describe everything as both a wave and a particle at the same time. This is what people refer to when they talk about photons - particles of light. These photons actually have momentum, which we can theoretically "collect" and use to move spacecraft with large solar "sails", much like conventional sails "collect" the momentum of the wind.
Just a bit of "basic" quantum for you to chew on.