Convert Spreadsheet into items to list on Amazon

I have a spreadsheet with over 20,000 different items. I need someone that knows the Amazon Inventory Loader: to convert my spreadsheet into files that I can use to uploaad my items to Amazon. Must have done this type of work before and understand Amazons Marketplace Templates. For anyone that knows how to do this is should be pretty easy to do. Let me know the sort of thing you have done before using Inventory Loader. Thanks