Hello puig18 - Could you elaborate a little more on your notes please? From what you have shared, it looks like you created an ebay account and already upgraded it to business account? But you haven't sold anything on ebay yet. First things first, a business account on ebay is gonna attract some running costs to you. If you haven't sold on ebay before or you are yet to research and find suppliers (which as the other Marc mentioned is where the bulk of your time should be dedicated to) I would personally recommend downgrading your account to an individual and save on the monthly running costs.
The first step of your research should not be identifying supplier but rather identifying products that might have demand in the marketplace you plan to sell in (in this case ebay). Without further information on what might be your area of interest, it is hard for anyone to provide any blanket advisory on how to proceed. In terms of identifying products to sell, zero in on your geographic target market first. For example - if you intend to sell in spain and spain only, then you might be in best position to judge what sells and what doesnt sell in spain. Like every other country there might be demand for millions of products.
A good starting point might be to start your research with ebay.es! Look for seller forums and read lotsa content on products that might be of interest to you. Then look up ebay for those product keywords and find out the prices at which they sell. Once this part is complete, then I would suggest hunting for suppliers.
Pick a product that you might have some background with to avoid any burn rate or expensive mistakes. The online market place is extremely competitive, but needless to say plenty of people succeed when they do things right. I'm happy to share more if you have specific questions in mind, do feel free to write to me. Would be happy to help. Good luck!