You can find an excellent calculator guide for the Casio FX991EX-ClassWiz on Dr Frost’s site.
From The Calculator Guide on YouTube see this comprehensive playlist on the Casio Classwiz fx-99EX. For example see this introductory video on using Statistics mode to find the mean, variance and other statistical summary data.
See also this playlist from Casio on the Classwiz FX 991EX.
From The Chalkface comes a brilliant spreadsheet that emulates the statistical functions of the Casio ClassWiz. The spreadsheet includes details which allow students to interpret each of the different modes, the List function is also included.
Direct link to the calculator.