In this case, it's all about the type of cream. Now, you really only need one ingredient to make whipped cream - cream (well, and air, too) - but it's crucial that you choose the right type of cream.
Light cream, half and half or whole milk will not work properly. In order for the cream to whip, it must have a high enough fat content, around 30% or more. Since different brands of cream differ slightly in the percentage of fat they contain, I recommend reading the labels to be sure. Generally, any "heavy cream" or "whipping cream" will work well. You will need about two cups for this recipe.