how can i make a blood appear from a body when a bullet hit it…
or when a bullet hit a wall how can i show on a halo in the wall??
Well have an empty follow your bullet and when it collides with the wall have the bullet end and the empty add a bullet hole to give the effect of it penatrating the wall… 
hope this helps
thanks.
another questions:
what is the definition of poly or low-poly and how can i now how much poly i have in model or in a scene and how much can blender have polys in a game??
To find out how many polys just look at the top right of the screen and faces its basiclly polys and i dont know how many polys blender can take i suppose it depends of yer graphics card and stuff.
sorry but where at the top right of the screen? i don’t find it…
The right end of the main toolbar on top shows vertex count. Next to “Blender 2.xx”
If you’re using Windows, then it should be over by the |_|? |x| buttons.
If you’re on a Mac system, then it should be on the opposite side of the screen, on the Y-axis.
I haven’t dealt with Linux before, but I’ve seen some screens and (unless you have it reprogrammed to look like Apple’s glorious OS) it should be like Windows.