At the moment, many of the community developers are providing advice which is good but also confusing. What you appear to do now is to learn how to code. The resources below may help you to understand what you need to do.
Learn to code.
Here are some resources to help you learn to use the AI2 tools. A very good way to learn App Inventor is to read the free Inventor's Manual here in the AI2 free online eBook App Inventor 2 Book: Create Your Own Android Apps ... the links are at the bottom of the Web page. The book 'teaches' users how to program with AI2 blocks.
There is a free programming course here Course In A Box and the aia files for the projects in the book are here: App Inventor 2 Book: Create Your Own Android Apps
How to do a lot of basic things with App Inventor are described here: How do you...? .
Also look here App inventor español. Offline. Tutorial. Ejemplos. Instalación. Códigos. Juegos. Curso gratis de App inventor. and here Tutorials for more tutorials including Imagnity.com List Tutorial, Mirrored - @Saj
Learn about components Component Reference
and visit the Library The MIT App Inventor Library: Documentation & Support Help>Library on the MENU
A tutorial using the Sound component and many files to display a lot of images.
You want to demonstrate a reading app for children which also teaches children how to spell alphabets and numbers. Also, the page where the sound component is not working has 10 other same numbers from 21 to 30 whose sound component is also not working. The Project below uses some code that is similar to what you hope to write.
It uses advanced techniques described in the pdf link that you might find useful in your Project.