Before creating your data, make sure you check the import setting of the website/shopping cart system you chose to use, just to be sure that it will fit the specifications and you will be able to upload it to your online shopping cart per system instruction, so that you will not be wasting your time and effort. The format for these files may vary, but you basically need at least to include columns for - the item number, product name, the description, the location of the picture for the product and the price.
Ask from the drop ship suppliers if they can provide you their inventory information in product data feed files. They would usually be able to provide these in CSV or other formats, and you may just convert it to Excel file (or they can provide it in excel file ready, saving you from the manual task), and you may use it directly to upload to your website.
I learned that Microsoft provides conversion methods (that you can use for free) to convert your Excel file to HTML . This will enable you to test your spreadsheet conversion and will allow you to see how it will look for your users. Instructions here Link hidden: Login to view
Hope this helps. :)