Bpsk demodulator implementation
You want to take a wav file, run it through a BPSK modulator and I'm guessing (from your #3) to plot some waveform or something. So you should find a wav file like handel.mat which is built into MATLAB, and convert it to binary. This may require some decisions like how many bits you choose to represent each sample if its not already something you can work with. 

All a modulator is doing is mapping bits to symbols. For BPSK, a single bit gets mapped to a single symbol (Bits 0 --> Symbol -1, Bit 1 --> Symbol +1). So now you have mapped to symbols. 

Now to make a plot you can just look at the equations for BPSK modulation and plot for some $f_c$ that you choose. Or, what I think you may have meant, is to plot the baseband signal in which case you then take your symbols, upconvert them, and pulse shape them (you'll have to choose some pulse shaping filter, check out rcosdesign() function in MATLAB).