When you list an item for the first time, you will need to provide your home address' postal code.
This step is required before your items can be activated and available for sale. Until then, your items are showing as Draft in your closet and buyers are not able to purchase them.
To add your postal code, you can go to your closet and click on Add postal code. You can also go to My account in your settings.
Make sure you type in the correct postal code as this will be used to calculate the shipping costs that your buyers pay when purchasing your items. Additional shipping costs aside from the ones initially paid by the buyer will not be covered by Vinted.