See
doc plot
for details and examples under the section 'Graphics/2-D and 3-D Plots' for Line Plots of Matrix Data
In short, a 2D array of y-values is considered separate variables for each column and the plotting is automagic. It only takes that the length of each is the same but this is also easily worked around by filling shorter areas with NaN which are ignored. Alternatively, use
hold on
and you can add subsequent information to the axes without losing the previously drawn. There are examples for this as well...
