By making games. There are lots of engines and frameworks these days to cater to people who want to create a game, but don't want to or can't do it from the ground up. Game Maker Studio and of course Unity come to mind.

I recommend a thorough read through the resources on http://www.reddit.com/r/gamedev as a starting point.

Same as with any position in the tech industry. It's not about job applications and education anymore. It's about networking. It's about demonstrating skills through projects. It's about online presence. It's about conferences and events. It's about reaching out to people who have done it before, and learning from them.

Depends, if you want to make your own idea in to a game start simple. Implement 1 core mechanic, you can't care about UI, Multiplayer, performance, or anything like that. Make a proof of concept, make it as simple as you can. Iterate.