Written a book before?

Have you ever written a book before? Do you have plans to?

I have written a young adult book and it's actually a series, so two of the three were self-published on Amazon. I didn't know anything about promotion, so it never really got sold except to friends.

Have tried but only thing I've finished is a middle part of trilogy and that turned out so short that the whole trilogy would more of make a book.
Must be over decade since I got into that project, started some 25 years ago.
I've really only written a few short stories, never published anything.