An author do not have to pay for a subscription, but part of the course cost goes to Stepik.
How to enable payment in US dollars you can find here.
7% of the sales goes to Stepik, remaining 93% is paid to the instructor (only if author's link was used before payment). Stepik can also help with promotion of the course: for example, If the payment is made from the catalog or search, 40% of the sales goes to Stepik, another 60% is paid to the instructor.
Read more about author link, which helps to determine the amount of commission charged for each purchase of a paid course.
If your course is in US dollars, Stepik transfers your share to your Paddle account after each payment, and you can choose when and how you will transfer them to your personal account.
You can see all the Stepik course sales statistics in Payments report in each of your paid courses.
Stepik does not assume any tax obligations for paid courses. After you transferred the money from Paddle, you must pay your taxes yourself on the basis of your taxpayer status and laws of the country of your residence.