Alright so, I am trying to make some textures/tiles for maptools, and I have so far done the first half right, I made the LOOK like textures/tiles. Now the only problem is, each and every one of them has a white or black background. So in order to correct that, I downloaded GIMP. Now the NEW issue is, I read the manuel to gimp, followed the instructions, and yet still cannot make the textures/tiles backgrounds transparent (or topdown or w/e it's called)

So please, help. How do I make things backgrounds transparent on Gimp? (The simpler you can make it sound, the better. :p)