It sounds like you're interested in using a drop-shipping app to sell apparel and merchandise online.
There are a number of apps which will support this for you. If you're looking to use your own designs, you may be interested in using Printful (https://apps.shopify.com/printful), Printify (https://apps.shopify.com/printify), or Merchify (https://apps.shopify.com/merchify). If you're looking to find products that are already designed, you may be interested in Oberlo (https://apps.shopify.com/ali) or Modalyst (https://apps.shopify.com/modalyst).
The way it works is that you would pick and setup your products via the app. These products would then be listed on your Shopify store. When a customer comes to your store and purchases one of these products, the order is automatically sent to the respective app which the product is set up through. You would need to pay the app the agreed upon price for the product, and they would handle the shipping for you. For example, the app may agree to sell or make shirts to/for you at $12 each, but then you could list these products at a higher rate, say $20 each for example, on your site. In this example, you would make a profit of $8 for that one shirt. All of these apps support shipping to anywhere in the world!
Hope this helps,
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