Problem with using a commando

To create a crossbar matrix for those points that we want to plot, we can use one of these ways:

P=[x;y]=[p1 p2 ... pn]

x and y are row vectors of length n of x and y coordinates points, while Pi is column vector with coordinates for a point. If we want to plot a curve with x and y coordinates with the commando:

>>plot(P(1,:), P(2,:))

But I really don't know how to use it, I mean, what values belongs to respective index?

For example if I have those coordinates: (0,1), (1,1), (0,0), (1,0) - where should I put these values in the commando?