Need help on compliation error.

Question

Hello to C# experts,

I need help with this compliation error:
Cannot apply indexing with [] to an expression of type 'object'

else
            {
                try
                {
                    OrderItem drinkOrder = new OrderItem("","",0,0.0m); // Referencing from a class within a package.
                    drinkOrder[itemCountInteger].quantityInteger
                        = int.Parse(quantityTextBox.Text);
                    if (drinkOrder[itemCountInteger].quantityInteger != 0)
                    {
                        drinkOrder[itemCountInteger].drinkString
                            = drinkTypeComboBox.SelectedItem.ToString();
                        drinkOrder[itemCountInteger].priceDecimal
                            = itemPriceDecimal;
                        totalOrderDecimal += itemPriceDecimal
                            * drinkOrder[itemCountInteger].quantityInteger;
                        drinkTotalInteger += drinkOrder[itemCountInteger]
                            .quantityInteger;
                        clearForNextItem();
                        orderCompleteButton.Enabled = true;
                        itemCountInteger++;
                    }
________________________________________________________________

those i highlighted in blue are those with the blue swiggly after i place in the code for referencing those variable from a class.

My tutor told the class to try it as a challenge but after i got to this point i am stuck, not sure how to continue this.

So really need some help from C# experts to explain to me how to solve so i will be able to solve it easily in future.