How do I start giving away the game?

1. Buy a game key. Due to region restrictions, gifting direct from Steam can be a pain anymore.
2. Select "Giveaways (upper left ), and use the drop-down menu to select "Create Giveaway."
3. The giveaway page itself is pretty self-explanatory. Fill in all the stuff, add a funny cat gif (or dog, per your preference) for the description.
4. Punch the Review Giveaway button (no, don't really punch it, just click on it, monitors are expensive!)
5. If all the information is correct, punch click on the Confirm Giveaway button.
6. Play some games, bake a cake, pick your toenails, or whatever else you like to do until the giveaway ends.

Once the giveaway is over (you'll get a pop-up on site when it ends), you click on the little gift/house icon in the upper right (or you can go to the giveaway itself on your profile), click on Winners, and send the lucky fellow the key to happiness!

Enjoy your stay and good luck. :)

[Ya know, all of this just made me wonder why there isn't a "Create Giveaway" button up top, unless it's due to space constraints.]

Well, you have good answers already, so welcome to SG. :D