If you don't have any bitcoins but you want to win some, you should try a free Bitcoin lottery. You can get lottery tickets every hour just by clicking a "claim" button without any annoying ads. I played this free Bitcoin lottery for about 2 years now and won about 0.2 BTC in total. In my opinion this is pretty much for a completely costless game and also I could have won much more if I had more luck.
Unlike normal lotteries, where the tickets cost a lot and you have virtually no chance of winning, this lottery costs nothing and you get additional free bitcoins every hour.