Rename the example mod project in Eclipse to the name of your mod.  This can be whatever, but please, please do not make a gem mod.

To open the actual code, open the project with the arrow next to it on the left, and navigate through src/main/java/ and src/main/resources.  These locations will be where we store our code and assets respectively.

In src/main/java/ there will be an example mod package.  We can delete this, as we will be making a mod without it.

Now we can make our own package.  Do this by right clicking on the java folder and hovering over new, then clicking Package.

Now let's make a main class in this package.  For the sake of simplicity, I will be calling it Main.

Now we will make a Reference class.  This is where we will store information about the mod for us to use throughout it's developement, such as the name and version.  I have created a util (short for utilites) package in my mod to make it easier to navigate in the future when we have much more code.

Now we need to add some variables to this class.  We need to include the mod's ID, name, version and path to our proxy classes.  It should look a little like this:

public static final String MOD_ID = "tutorial_mod";
public static final String MOD_NAME = "Tutorial Mod";
public static final String VERSION = "Alpha 1.0";

public static final String CLIENT_PROXY = "club.mcmodding.tutorial_mod.proxy.ClientProxy";
public static final String COMMON_PROXY = "club.mcmodding.tutorial_mod.proxy.CommonProxy";

Now open your main class, and add the @Mod above the class name, which will accept the variables we entered into Reference.  It should look like so:

@Mod(modid = Reference.MOD_ID, name = Reference.NAME, version = Reference.VERSION)
public class Main {

}

Now we need to create an instance of our main class like so:

@Mod(modid = Reference.MOD_ID, name = Reference.NAME, version = Reference.VERSION)
public class Main {

    @Instance
    public static Main instance;

}

Then we will make a sided proxy like this (ignore the errors, we have not made the proxy classes yet):

@SidedProxy(clientSide = Reference.CLIENT_PROXY, serverSide = Reference.COMMON_PROXY)
public static CommonProxy proxy;

Next create a proxy package in your project.  This must be the same name as what you put in your Reference file:

In this case the package would just be club.mcmodding.tutorial_mod.proxy

Now, in that package, we must create the two classes ClientProxy and CommonProxy.  ClientProxy needs to extend CommonProxy.  Other than that, both can be left alone for now.

Finally (phew), we will create three initialization events like so in our main class:

@EventHandler
public static void preInit(FMLPreInitializationEvent event) {

}

@EventHandler
public static void init(FMLInitializationEvent event) {

}

@EventHandler
public static void postInit(FMLPostInitializationEvent event) {

}