As a small producer you are able to set the quantity available to buy for each of your products.
It is important to manage your inventory correctly in this way to avoid disappointed customers and refunds which will also in turn harm your ranking in the marketplace.
Likewise keep an eye on when your Available to Buy quantities are running low so that you don't miss out on sales.
Setting your inventory levels
To set your inventory levels see the Available to Buy (or Quantity) fields in your editable listings.
If you have different size options for a listing you can specify the inventory level for each size variant. To do this make sure the specific option has the Inventory field checked, the Inventory field for the listing as a whole is set to "Track with Options" and then you will find the Available to Buy field can be specified per variant.
Made to Order items
If you make items to order then you don't really have a stock level but you could use the Available to Buy as a way of limiting sales to volumes you are comfortable with at a time. Obviously then you will need to make sure you come back regularly and replenish the quantities.
Generally speaking if you make to order it is best to just set a relatively high Available to Buy number that represents 2-4 weeks worth of orders you can manage and you can see how it goes.
Out of Stock
Your sales will erode the inventory number you have set and once it reaches 0 your product is classified as Sold Out. You will receive notifications before your product reaches 0 to give you advance warning.
Always remember to set the Available to Buy quantity manually to 0 if you are temporarily out of stock. If you have permanently discontinued a product or it will be out of stock for more than 2 months change the listing status to Disabled (you can always reactivate it down the line).
If you have an item that isn't available to ship yet but you know when it will be then you can start offering it for sale on a pre-order basis. See the guide here.