If you have any experience with modding for Minecraft you will see that a lot has changed.
To start modding you will have to open the “Minecraft” folder on the top left. This will open a lot of new maps, but most of these are not important. The only ones that are important are src and common folders. The one you should open right now is the common one. This will open a lot of packages.
The ones that are called: cpw.mods.fml.something are all from FML. FML is a part of forge.
Net.minecraft.server is the package that contains the MinecraftServer file. You will not have to use this at all if you program the way you should.
Everything that starts with net.minecraftforge is from Forge. You will not have to add any files to these packages, but you should use them to find out how methods in forge are called.
All the packages that are called: org.bouncycastle are also not used for your modding.
The most important package is the net.minecraft.src package. In here are all the files used by the Minecraft server and client.
When you open the src package above the common one you will see that this folder also contains several packages.
The packages starting with cpw.mods.fml are the client sided things from fml. These are mostly things like rendering (showing the world) and sounds, because those 2 things are only client side and are not on the server.
The same for all the net.minecraftforge package.
Paulscode.sound.codecs and ibxm are both also used for music.
There are 2 packages left. The first one is net.minecraft.client. This is the client version of the net.minecraft.server package. It contains the minecraft client files. The last one is net.minecraft.src. This package contains all the files specific for the minecraft client. Most of these files are for rendering and sound.
In the next tutorial I will explain how to actually make your first mod file.