Well, first you need to find the 'Post' or 'Submit' button on the website. Then, after posting one story, look for a similar option again to post another. Some sites might have a limit on how many you can post at once, though.
Yes, you can post your own stories to your own website. Just make sure you have the necessary technical setup and maybe consider some aspects like design and navigation to make it user-friendly for readers.
Medium is also a decent choice. It has a wide audience and some writers' communities where you can post your stories and receive valuable critiques. Just make sure to engage with the community actively to get more responses.
It depends. If you're just starting out, maybe once or twice a week to build an audience. But if you have a lot of content ready, you could post daily.