Giveaway question

You can't enter in the giveaweay, if you have the game

Once you give it, you lose that copy.

Be aware, the inventory isn't the same as your library.

Library can't be gifted.
Inventory can.

Three options:

1. Add the person to your friend list and give the game directly through the steam trading window.
2. Add the person and in your inventory use the Send Gift button and send it directly through steam. You will keep the gift in your inventory until it is redeemed.
3. Use the Send Gift button in your inventory and send it by e-mail. You will also keep the gift in your inventory until it is redeemed.

yes it does, if you are talking about your library then no you can't giveaway games that you have already used