Questions while studying events

I saw codes like this in ItemBow's code:

    public void onPlayerStoppedUsing(ItemStack par1ItemStack, World par2World, EntityPlayer par3EntityPlayer, int par4)
    {
        int var6 = this.getMaxItemUseDuration(par1ItemStack) - par4;

        ArrowLooseEvent event = new ArrowLooseEvent(par3EntityPlayer, par1ItemStack, var6);
        MinecraftForge.EVENT_BUS.post(event);
        if (event.isCanceled())
        {
            return;
        }

    public ItemStack onItemRightClick(ItemStack par1ItemStack, World par2World, EntityPlayer par3EntityPlayer)
    {
    	
        ArrowNockEvent event = new ArrowNockEvent(par3EntityPlayer, par1ItemStack);
        MinecraftForge.EVENT_BUS.post(event);
        if (event.isCanceled())
        {
            return event.result;
        }

Judging from the code, I think those two events' function is to determine whether the movement of shooting arrow is normally continuing, if not the arrow will not be shot and action is cancelled.

but the two events' classes are so simple that I don't really understand how the func is done.

Question 1 : When and where are the events "setCancel"ed, and how does Forge EventBus handle this during the player's movement?

Question 2: How do I do similar task in my Items? Do I need to just simply copy and paste the event code and do "MinecraftForge.EVENT_BUS.register()"?

Question 3: What can I do with events mainly ?

Thanks a lot for you time of reading this topic and answering