Simple Question on Wavrecord Syntax & Correlation Syntax

Hello, I have read this Matlab link on wavrecord http://www.mathworks.co.uk/help/matlab/ref/wavrecord.html I want to ask what is the y axis, they say it is n samples of audio signal but

1. what is the unit, it is voltage, power density?

2. And the unit for x axis for the graph when I put plot(y); after the first command? It is Hz? "y = wavrecord(n,Fs) records n samples of an audio signal, sampled at a rate of Fs Hz (samples per second). "

3. How does the correlation command in Matlab works, it uses the formula shown in the link below R(i,j)=...? http://www.mathworks.co.uk/help/matlab/ref/corrcoef.html