If you are a professional programmer but are unfamiliar with the Ada language, a good hands-on way to gain familiarity is to go to Ada Barebones which is a back to the basics informational site that takes you step by step through the basic development process.

To use the tutorial effectively you should have a compiler which can handle ELF files and use it to build a GCC which targets i386-elf or some other similar architecture.

This is one of a number of web pages on a Wiki maintained by OSDev.org,  a website which provides information about the creation of operating systems and serves as a community for those people interested in OS creation..