As you see the picture above its the cobblestone generator, but lets just make a written tutorial.

First dig out 4 x 1 with 1 block deep and should look a little some thing like this :

1 2 3 4

now on number 2 dig another block down by 1 so on number 2 it should be 2 blocks deep.
put water on number 1 and lava number 4 on number 3 is the place where cobblestone generates.
and your quiet done

if you're lazy to mine it manually make an accel war gate (i think thats the name), it will make a blinking redstone and attach the blinking redstone to a piston facing to number 3. i believe there's a tutorial video on how to make the blinking redstone.

if you're on SMP and you're friend want to mine as well, make it like this:

1 2 3 4 5 4 3 2 1

on number 1 put lava,number 2 make it 2 blocks deep,number 3 leave it empty for the cobblestone generate,number 4 is the location where the lava will flow and put the lava on number 5.

leave a comment for more tutorials. I made this post originally from me :)