Greetings, @Pozo!
Always good to see a new face.
First, you will need to get Author status. Click on Store on the red bar at the top of any page on the site, and take it from there.
I see @Myr has already given you the link to the entry about how to post Stories to the site. It may seem a bit complicated at first, but it's really just a case of following each step in turn.
@Renee Stevens' first post in the following entry in the Writer's Circle Anthologies forum goes through all the steps for submitting an anthology entry:
(Ignore the due date of 15th November. As you know, that has been extended to the 30th.)
Finally, you might want to consider joining the Writer's Circle Club, if you haven't already done so.
https://gayauthors.org/forums/forum/274-writers/
I look forward to eventually reading some of your writings.