What you have said is correct. Appendices go after the References section, and are titled "Appendix A", "Appendix B" etc. You might be able to use numbers instead if you wish, but I only see published reports with lettered appendices.
All you need to do in the actual appendices is insert the image/chart you are referring to in-text and cite it as "Appendix A shows that..." or whatever you need to do to make it understandable. Make sure you title it, to explain what it is, for example "Appendix A: A bar chart showing...". Don't put appendices in reports and expect them to be self-explanatory, you must cite them in the main body of your report and explain how they contribute.
If you created the images/charts yourself, you don't need to reference them in your References section, but if you got them from another source you should. Put a citation underneath the image/chart if the source is not yours.
For example, in one of my assignments I had to put a questionnaire I did not design in the Appendix section, and I cited the authors and the date underneath it so the reader knows it didn't come from me.