In the onEnable method

new InventoryBuilder(this);

Create a Inventory

InventoryBuilder builder = new InventoryBuilder("Test Inventory", 9,Main.getPlugin());

Set a Item in the inventory with a action

builder.setItem(0, new ItemStack(Material.CAKE), new InventoryBuilder.ClickEvent() {
    @Override
    public void press() {

    }
});

Set a Item in the inventory without a action

builder.setItem(4,new ItemStack(Material.STICK));

Make that player can/cannot move the items

builder.setMovableItems(true/false);

Open the inventory to a player

builder.open(player);