Please excuse my answer is in English. I do not speak French, but I was accidently the first one who would answer your question.
1) When you add axes into canvas, you would get object names for each axis. By default, the axes will have their names "app.UIAxes", "app.UIAxes2", etc accordingly.
2) You can pass these axis objects to functions. For example, plot provides options to use axis as its first input argument in order to specify in which axes you want to plot graphes.
plot(ax, ___ )
Hence, for example, if you would want to plot a graph on the first UIAxes, you can code something like this:
x = 1:10; y = 1:10;
plot(app.UIAxes, x, y); % instead of only plot(x, y);
