What you're describing is a callback function that adds a point, here are the ingredients you'll need:
- a callback function: something to detect that you've clicked and give you a place to write code. ButtonDownFcn on the axes will do the trick
- a way to get the place where the click happened, the CurrentPoint property of axes will work for this.
- plot!
ax=gca;
plot(rand(1,10)); % just plotting something, but totally not required
hold(ax, 'on'); % just turning on hold because I'll assume that you don't want the axes reset each time you plot another point
ax.ButtonDownFcn = @(~,~)plot(ax,ax.CurrentPoint(1,1),ax.CurrentPoint(1,2),'ko');
Tiny bit of warning, you might get into trouble if you have something else in your axes, like an image or another plot that grabs the click. The HitTest property can be useful here - this documentation page has more info: https://www.mathworks.com/help/matlab/creating_plots/capturing-mouse-clicks.html
