Reading books. There are some great books on programming out there. I would strongly recommend a A Players Guide to C#. It's structure, practice problems, and explainations of the basics were far better than any free guide to programming that I've seen online. There are a lot of other great books out there too.
It also doesn't matter too much about a book being outdated when you are only studying the fundamentals.
A lot of the stuff you read online has never been fact checked or edited for clarity. Some of it is great, but most of it is not.
It's actually pretty good for a mobile game, it scratches that civ itch in 30 minute long games.