What happens when you win a game?

A notification pops up on the website (it is displayed on every page) telling you you won it, and asking you to mark it as received when you receive it. The gifter also receives a notification that one of their giveaways has ended; the gifter can access & will send their gift to the email address you have saved on the website.

If you do not receive a gift, after 7 days you can mark a gift as "Not received". We ask that you try and contact the gifter (via Steam) before doing this; I'd say a reasonable time to wait before contacting the gifter would be 24-hours after a giveaway has ended. Similarly, if a gifter has sent a game and it is not redeemed after 7 days, we consider it appropriate for a gifter to reclaim that gift.

As far as I know, email notifications are currently not implemented within the website. I do not know if they will be, but they would certainly be very useful.

It descends from sky into your steam computer taking the form a another steam user and then a window pops up.
-experience may vary