How to with graphic png blocks and items 3D/2D

[MrNice]

Hi i am new one.

I like to make a mod so much but there are so many nasty things in him. Well my problem is how it is done that from 2D textures terrain, chest,largchest in minecraft.jar about {16x*/16x*}xx=256x* are made 3D/2D things items??(pistons, doors 32/16), how the code know what to do where or how specify draw a current png file into 3D/2D.

Pls help me i wanted to try make some my own mod but this basic thing screews up evreyting. For instance if i wanted to make some blocks that are smaller than default in minecraft or make some fancy large thiny construcion, also what determines the block orientetion like in pistons.

Thx for help.