Box Plots show summary information for data – the box shows the median and quartiles and the whiskers are extended to all points which are not outliers.
A very clear description for younger students can be found on BBC Bitesize. For A Level Students the Centre for Innovation in Mathematics Teaching includes Box Plots in Chapter 3 of their Statistics text (page 26 of the pdf file, which is page 76 of the text).
Box Plots are particularly useful when comparing one or more distributions;
To help older students think further about about outliers and skew, have a look at this excellent illustration of Nobel Prize data from Plotly. Who is that outlier for the Nobel Peace Prize?!
Note that it is possible to display points with Box Plots in Plotly, the following data and charts demonstrates skew well:
You can learn more about Plotly for graphing and sharing your data here: Learn and explore Plotly