Give the opportunity to your customers to customize items when they order. You can create multiple options and choose if they are for free or at an additional charge.
Create an Option for users to Add Ice Cream.
Create the Items under that option with any additional charge shown: Vanilla (+1.50), Chocolate (+1.50), Caramel (+1.50).
Create an Option: Go to My Stores > Click Manage Menus next to the store entry > Click Menu Items next to the menu entry > Click Create Item Options on the top right > Select Add New Item Options > Give it a name (eg. "Add Ice Cream:") and Save.
Create an Item: Go next to the Option you just created and click Item Options > Click Add New Item on top right > Enter name (eg. "Vanilla") and details and Save. Repeat this step to step add more options.
If the options under this category are for free select the Free ON
If these options are charged extra set the additional charge.