Carefully thought graphs and diagrams can help you make your point. R has very nice features when it comes to graphs. Nevertheless, things can get cumbersome quickly.
This first link provides a good explanation on how to make simple graphs. This other link contains an encyclopedic treatment of graphs in R.
Finally, in the event you are using R Studio and the plot refuses to show up, go to the Console and type “dev.off()” till you get an error message. Then, try plotting the graph again. Another solution is to restart R Studio. More on this issue can be found here.