A Boxplot is an exploratory graphic that allows you to summarize the features of quantitative variables for one or several levels of a discrete variable. Here is a small visual to help you remember what the different parts of the boxplot mean.
The Flowing Data Website provides this sheme and gives clear explanations with an easy to understand “hamburger” exemple.
R provides everything you need to make the boxplot you desire (using the boxplot function), and I hope you will find the exemple you need in this gallery ! If not, don’t forget to ask or contribute !