Is there lessons？
See
Yes. In addition to those already posted there is a free on line course and book:
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 http://www.imagnity.com/tutorial-index/ 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