So i read the FAQ. But i did not fully understand how it is, you know you have won.

Can't take a screenshot right now, but I can explain how it looks. When you go to your homepage, there is a green banner above all the giveaways, it's very hard to miss, and it says that you have won one of the giveaways you have entered. Similar to this is a banner that tells you when your giveaway has ended.

Another way of seeing whether and what you have won is in the won section.

aww If i read it 2 hours ago, I probably get the screen :|

The next time I should take the screen <.<

This is how the winner bar looks like // This is how the ended giveaway one looks like
To all of those says you can't take a screenshot, you CAN un-tick a tick-box on your won giveaways page.