First don't panic :)
Most people don't know exactly what their items weight. If you don't know the shipping weight then just make a rough guess so that you can get a estimate of how much the order will cost to ship. I have a button on my order page that will help you calculate the shipping weight if you know the approximate size of your item. Don't be too concerened if you estimate too high or low as it will does not affect the final shipping cost in anyway.
Some good places to find the shipping weight of an item is amazon and walmart as they normally list the shipping weight for their products. Please keep in mind that this information is not always 100% accurate and that they may also not list the correct shipping dimensions. Walmart seems to be more accurate than amazon, but it caries a smaller number of items.
If you still have no idea of the item(s) weight then choose one of the "estimate shipping for me" options from the drop down menu. We will then use out experience to try and estimate for you. It helps us help you if you can provide the size of each item in the order details. If you only have a rough idea even providing this will help us to give you the most accurate quote possible.