All Casio manuals and other resources can be found on the Casio website here.
See the CG50 page for example. An extensive resource collection is available for the calculator – Use the filters to refine your search – look at Subject for example. I do like Casio’s Quick Start Guides, 28 pages for the CG50 giving a great overview (the complete manual has 600+ pages!)
Videos can be very helpful and I have successfully used many videos from The Calculator Guide in class.
From Pearson-Edexcel, one of their excellent guides from the Teaching and Learning Materials collection, we have this guide to using calculators when teaching AS and A level Mathematics. This very clear 5 page document lists specification content for AS and A Level Mathematics and provides video tutorials for a Scientific Calculator (Casio ClassWiz) and a Graphics Calculator (Casio CG50).
For older students (16+) MEI have created tasks using Casio Graphical Calculators as part of their excellent series of resources on Integrating Technology. Note that the series includes many tasks for the excellent, free GeoGebra and Desmos.
(There are pages on this blog on GeoGebra, WolframAlpha and Desmos.)