Convert a Template to a Website

I have an e-commerce tire website that I need to add my own product to. I have the data for the products on paper. I would need you to add the data, pictures, and so forth to the site so people can find it when they search for those sizes. There are about 100 different sizes. I don't know the software they used to build the site but I have access to the back end and there is a section where you can load your own product. So you would have to transfer the data from paper to excel and then upload it. Then I have products that I need to add that we can download the spread sheets from online, and upload them. Total manual products would be around 100-150. The other brand there's about 200 sizes but spreadsheets can be downloaded, but the pricing you would have to put on the spreadsheets manually, I would supply pricing.