If you just want to put a title over multiple subplots, you can use sgtitle().
If you want text in a box with arbitrary location, you can use annotations.
[x y z] = peaks(30);
subplot(2,1,1)
surf(x,y,z,'facelighting','flat');
camlight
subplot(2,1,2)
surf(x,y,z,'facelighting','gouraud');
camlight
annstr = sprintf('blah blah\nblah'); % annotation text
annpos = [0.1 0.1 0.1 0.1]; % annotation position in figure coordinates
ha = annotation('textbox',annpos,'string',annstr);
ha.HorizontalAlignment = 'center';
ha.BackgroundColor = [0.9 0.5 1]; % make the box opaque with some color
The other properties of the annotation can be set as needed.
