A lot of documentation is available on the internet, here you will find useful links, with a small description, divided into sections:
The Reference Manuals
Welcome to the hypertext Ada83 LRM (version 2.4). You may enter the document by selecting an entry point below. An interactive index is in the works.
This is KSCE's hypertext version of the Ada 95 Reference Manual (Language and Standard Libraries), revised international standard (ISO/IEC 8652:1995): Information Technology — Programming Languages — Ada.
Ada 2005 Language Reference Manual
The documents on this page consolidate Amendment 1 to Ada 95 with Technical Corrigendum 1 and the Ada Standard (International Standard ISO/IEC 8652:1995). The Amendment was produced by the ISO/IEC JTC 1/SC 22/WG 9 Ada Rapporteur Group (ARG). These documents are not an official publication or work product of the ARG, but rather are provided by Ada Europe as a service to the Ada community.
The development of Ada 95 and Ada 2005 would have been impossible without the strong foundation provided by Ada 83. As part of the numerous rounds of edits on the Reference Manual, the acknowledgments regarding the design team for the original language were unfortunately omitted. We apologize for this omission. The acknowledgment section for the Ada 83 language can be found in the Foreword of the Ada 83 standard.
Ada 2012 Language Reference Manual
The documents on this page consolidate a possible second amendment to Ada 95 with the previously standardized Amendment 1, Technical Corrigendum 1, and the Ada Standard (International Standard ISO/IEC 8652:1995). The Amendment (Amendment 2) will be produced by the ISO/IEC JTC 1/SC 22/WG 9 Ada Rapporteur Group (ARG). The final form of Amendment 2, or whether its standardization will succeed, are not known at this time. Thus, any proposed feature may be substantially changed or withdrawn before the Amendment begins standardization. These draft documents are not an official publication or work product of the ARG, but rather are provided by the ARA as a service to the Ada community.
Tutorial
This tutorial teaches the entire Ada 95 dialect of the Ada language. It is composed of 33 chapters which should be studied in order since topics are introduced in a logical order and build upon topics introduced in previous chapters. It is to the students benefit to download the source code for the example programs, then compile and execute each program as it is studied. The diligent student will modify the example program in some way, then recompile and execute it to see if he understands the material studied for that program. This will provide the student with valuable experience using his compiler.
Ada Programming tutorial at Wikibooks.
This is the first Ada tutorial covering the Ada 2005 standard. If you are a beginner you will learn the latest standard — if you are a seasoned Ada user you can see what's new.
Here you will find links to tutorials specially made to learn the Ada programming language in all its glory. These tutorials offer an alternative to the classic learning methods in that they offer an interactive means of letting you learn at your own pace while testing the knowledge you already learned.
As everything in Ada World, there's always room to grow, I might not have every single tutorial there is, but it is my goal, so feel free to let me know of tutorials you can't find here so I can update this list.