I'm new, please help with giveaways.

if you have a giftable game in your inventory you can create GA with it. If you have a game in your library you cannot give toi t anyone anymore, so you have to buy other game to give it away.

I already have a game in my gifts
If you mean you're trying to give something away, it needs to be in your INVENTORY. Basically you can't give away anything in your LIBRARY. The giveaway portion on this site is not synced with your account, so you can put as many copies as you want of any game that you want. Provided you deliver at the end, of course.

Game in your gifts? Does that mean your inventory? You need to trade/gift the copy you have in your Steam inventory to the winners of your giveaways.

"if I already have a game in my gifts" << what do you mean by "gifts"?

You can only give away copies from your inventory, not from your library.
You're also allowed to give away unused Steam game keys.

Oh, I meant my inventory, yes. So it should work, thanks for the help.

Welcome to all those who are new to steamgifts, by the way.
Just joined last night, myself ;)