I don't understand, can i download it for free and use it on my project ? then can i sell the game ? or not i mean sell in steam or to someone or somthing like that, is anything req for me to do so in free ? like giiving credit or paying or what ?
Yes, you can download the free sample and use it in a video game, and sell that video game on Steam. You are not required to credit me.
There's a link at the bottom of the page called "Mana Seed User License" that explains everything in more detail, as well as additional restrictions that may or may not apply to your game.