It’s important to note that by the time Austen tries her hand at writing novels, in the 1790s, writing novels is not such an unusual thing to do. There are a lot of novels around and she herself has read a lot of novels.
However, she’s unsuccessful in getting her novels published. We know that an early version of what became Pride and Prejudice was sent to a publisher and returned unopened, or certainly unread. Her short novel, Northanger Abbey, or, again, an earlier version of it, was purchased by a London bookseller but then never published. (Because he’d purchased it, the bookseller was quite at liberty not to publish it.) She wrote an early version of Sense and Sensibility called “Elinor and Marianne”, but again, it didn’t get published in book form.
So, there were these early, unsuccessful attempts, in her twenties, to become a novelist, as it were. In some ways, that was actually quite lucky for Austen, and maybe lucky for us, too, because it meant that when she came back to trying to write novels a decade later, in her mid-thirties, she’d already had lots of practice. She’d tried things out.