Action Details
Requirements and how-to articles for Etsy's action:

Once your shop is set up, you can list the items which you have available for sale.

You need this to get it done:

A short but descriptive title for your listing (maximum of 140 characters.)
"About this listing"
Choose whether your product is Handmade, Vintage or a Craft Supply, who made it, what the item is, and when it was made.
Photos of the product you are offering in your listing.
Dimensions: Should be at least 2000 pixels wide. (Buyers like to zoom in on photos to see item details, so don't scale your image down to a smaller size.) Height can vary, but try and ensure that the first photo in a listing is either horizontal or square. It's also recommended to try and make sure all of your images have the same dimensions.
Thumbnail images on search results and shop pages are automatically resized to 75 x 75 pixels, and images on listing pages are automatically resized to 170 x 135 pixels or 155 x 125 pixels (cropped from the centre of the image.)
Etsy recommends using at least 5 images.
You can also add more photos if you have different variations of your product(s.)
Attributes (optional)
If you wish, you can add attributes to your listing to help buyers find it more easily, such as colour or occasion.
Listing Categories
Choose which category your item belongs to (e.g. jewellery/prints/books/etc.)
Renewal Option
Listings stay up on Etsy for 4 months at a time. You can choose whether it is automatically or manually renewed.
Item Type
Select whether your item is physical or a digital file(s.)
Write a description for your listing which tells your customers all the information they should know about it.
How much your item costs (this will appear in your preferred currency.)
Note: Sellers in the EU will see an extra field to input a price per unit.
If you have multiples of the same item, you can add a quantity value which decreases as stock is purchased.
Delivery Options
Choose the delivery profile you wish to use for this listing.
Files (if digital listing)
If you have a digital listing, you must upload the file(s) for customers who purchase it to download.
Maximum file size: 20MB (for each file)
Supported file formats (audio): .mpeg/.mp3
Supported file formats (image): .gif/.jpeg/.png/.tiff/.bmp/.pdf
Support file format (text): .txt
File names are limited to 70 alphanumeric characters, periods, underscores, or hyphens.
Note: Digital items cannot have variations.
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How-To Articles
A list of useful links for you:

Etsy Help Centre - What Are the Requirements for Listing Photos?
Official requirements for listing photos on Etsy.
Etsy Help Centre - How to List an Item in Your Etsy Shop
Official information about listing items on Etsy.
Etsy Help Centre - How to List a Digital Item in Your Etsy Shop
Official requirements for digital listings on Etsy.
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