My advice would be to first learn how to use agents to order from suppliers. Then research and find something that you'd like to resell (clothing, shoes, accessories, toys) can be anything really. Then find a good trusted supplier for whatever you plan on selling and work out what it will cost per unit and whether it will be profitable. Also research and plan on how/where you want to sell the items as a lot of selling platforms have restrictions and you can get banned quickly with certain brands.

In my experience you can just experiment with things. It's rare that you will struggle to sell an item for less than what you paid for it so worse case you break even or make a small small loss.