ecart-add to cart

I am creating a new cart.
I have a product and size/price selection for an item
I would like to have a check box for additional item, gift wrapping that i want to add the price to the selection if the box is ticked and then show this and the total price in the cart.
I have been trying to use an updatable check box. I cant quite figure out where to put it, in the form field with the "Add to cart Button" or Outside the form field? anyway I choose I cant get any info from the button.
In the checkbox inspector I dont understand the area "Check if" I dont know what to put there, and I dont understand the Equal to text area as well.
I have a Gift wrap column in the cart details. I have a gift wrap table in the data base, separate from the main product data base table.I have also added the Gift wrap to the price calculations see pic
I cant get it to work, can you please point me in the right direction.
Thanks David