Mass upload products from csv excel files to my ecommerce store

I have this ecommerce "zen cart" website with the add on called "Apsona Shopadmin". I need help to seperate products from 3 suppliers into different new main categories. 2 Of these suppliers shoud be clearly marked that ship world wide. 1 of these (the biggest) should be clearly marked that ship to UK and Ireland. Then, I need you to mass upload the products from 3 excel files into the right places and tell me how, so I can upload this myself next time without any errors and specify the "columns" and/or add what my excel sheets asks for. Modify whatever needed for my products to ship to the right teritory, so I dont need any other changes or adjustments to start selling.