[Jtsummers]

It'll take you less than a week to get proficient enough in it to make something useful, or at least interesting. It's a very straightforward language, overall.

https://learn.adacore.com/ - Pretty much the best free source until you're actually ready to commit to the language. The "Introduction to Ada" course took me maybe a week of 1-2 hours a day reading and practicing to go through. There's also a SPARK course that takes a bit longer, but is also interactive.

The language reference manuals for 2012 and 202x (which should become Ada 2022):

http://www.ada-auth.org/standards/ada12.html

http://www.ada-auth.org/standards/ada2x.html

[touisteur]

Also, don't hesitate to use Rosetta Code to find useful little snippets. Not all perfect but a good jump-start.

[Jtsummers]

Yep, I wrote a bunch of those RC examples too. It was a useful exercise when I decided to learn Ada (and with other languages, too).