Today is the day you can grab the mobile hit Fallout Shelter on your PC. So how do you do it? Well, right now it's only through Bethesda.net. If you have an account, you can go there to pick up the game.
As for when it will hit other means of distributions, we don't know as of yet. The mobile versions got a big update yesterday introducing quests, new enemies, and a new combat system. I was surprised at how much more interactive it got as now I can't just send my dwellers out into the wasteland and just shut down my tablet.
There's also a nuka cola option now where you can spend X amount of nuka cola to immediately see go to an event such as a quest or heading back to the vault.
So pick up your version of Fallout Shelter now for the computer or update your mobile version for some new Fallout fun.