All Casio manuals can be found on the Casio website here.
See the CG50 page for example. Scroll down for Skills – Learn how to use the CG50, see 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 found the videos from The Calculator Guide very helpful.
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.