dose giveaway give me a rep points ?

Scammers will contact you no matter what. But if you don't have any rep, then you're an "unknown" and people are less likely to trust you.

then you mean trade feedback - and as it's name is suggesting it's associated with your trades not giveaways.

best way to quickly earn quite a lot of feedback is to trade bundle leftovers with other experienced traders - your leftover they don't have for theirs leftover you don't have. In such trades you don't risk a lot of money, as those games are usually worth just few cents, but you earn rep. and +rep from trade of items worth 0.1$ is worth the same as +rep from trade of items worth 60$ ;)

When you give a game away for free here, you get CV which allows you to enter higher level giveaways which means less people can enter them giving you a better chance to win a free game.