Your English is excellent, you should not be apologising for it.
Drawing a graph is done in cairo. You will have to make a customised widget. There's a tutorial on this in the Gtk website. Text direction is done by applying a rotation matrix.
Drawing a gaph is actually quite an easy task, it just requires a lot of code. A year ago I wrote a package for plotting line graphs that you could disect and turn into a bar graph widget. There's lots of features that you probably don't need (multiple plotting, handling four quadrants, wiggles on the axes, zooming and autoscaling) and will cut out as well as the actual drawing will be different for the bar look, but it might provide a good framework to get started; though I have to apologise as the code is very long due to the many if then else scenarios (I like to optimise so I avoid putting 'if's in for loops) and lacking in inline commenting.
The code is in gtk2, but as it uses cairo there's not much work neeed to bring it into a gtk3 format.https://github.com/pchilds/GtkPlot/tree/master/PlotLinear
Let me know if you need any further advice,