hello i am making a Gun's game just like Doom3 and stuff like that so look i have builded the world but i got a problom when i load the BMP texture of the gun it have a black background so its i'm moving in the world with my gun but my gun's background is black how do i make it without the background of it? so i'll see only the gun and my 3d world? thx

Dont use bitmaps change to tga.
you need to look around for information about alpha blending.

try nehe tutorials

Neon

Look at lessons 32 and 33

To add to what unfinished said; there are many other image formats that support transparency, but nehe has code for tga. You'd be better off using alpha test than blending - essentially it tells opengl to ignore any pixels with an alpha value lower than a certain amount, which is exactly what you want (or will, once you've got your bmp into a format with an alpha channel). There are other ways to do it, but this is the simplest way to do what you want.