To create a shop visit the help center (you can just search something along the lines of, how to create a shop) there you just click the link it says to create one
In the help center there is a section specifically for shop related questions you could look through for more additional info if needed.
Thereās no listing fee for posting patterns, however should you choose to sell a pattern a small portion goes to Ribblr and Stripe. Stripe is the only acceptable way for Shop owners to sell their patterns however you can post free patterns without having to pay anything. There exists somewhere called a SelFee where that fee thatās paid to Ribblr/Stripe becomes smaller based on who clicks the SelFee link you share (A specific pattern or the shop)
As a shop owner any patterns (whether itās a draft or posted) can be tested by users here to make sure itās understandable, feel free to look at the testing guidelines if that interests you. Thereās other features available so definitely take a look through everything when you have the chance! Sorry for the long post even if most of it was additional info you didnāt ask for I hope it explains some potential questions you may have later down the road!