If you're trying to showcase your writing skills, either for fiction or for nonfiction, then you need a writing portfolio. Writers of fiction can make use of a writing portfolio just as freelance writers do. Be careful though that you don't post something that affects its intrinsic value if you wish to market the rights at a later date.
As I stated before, I don't bother with the online portfolio sites to display writing samples and showcase my writing skills because the sites are cumbersome to navigate and take far too much time in uploading content. Plus, it's just more URLs and passwords to have to remember.
I've always thought it was far easier to set up a website or blog and use that as your online portfolio. That way you control the content, the URL, etc. The portfolio site can't suddenly change its Terms of Service and commandeer ownership of what you post. (Sure, Facebook failed in their recent attempt to claim ownership of posted content, but who has the time to mount these campaigns to make a site back down?)
You know how much I love blogs, especially because you can use your name for the blog and that will be your URL i.e. MaryJones.blogspot.com or BobJonesFiction.blogspot.com. A name is much more appealing than a portfolio site with your identity being a string of numbers.
Blogspot is the easiest platform I've used, and it can be personalized so it will be memorable. Plus, it's so easy to update.
You can create a portfolio either on an existing site or a separate blog to showcase your fiction too.For a fiction portfolio, make your categories fit the work. For instance, if you're posting a novel that has been flogged from here to Estonia with no takers, and you just want someone to read it, then post it chapter by chapter with your Labels being Chapter 1, Chapter 2, etc. Then maybe have a category in which you analyze why you think the manuscript didn't sell or what you learned about writing from that manuscript or maybe collect the comments about it in a category.
When you talk to other aspiring novelists or industry professionals, you can point them to your portfolio. (Fiction is such a different kettle of fish that you have to analyze every action when dealing with industry professionals like agents and editors to make sure you're not making a misstep. Make sure a fiction portfolio does NOT look amateurish in case you do want to show it to an agent.)
Basic Rules For Fiction Portfolio
1. Figure out what kind of fiction for which you want to be known.
2. Make your Labels or Categories reflect those niches i.e. chapters of a novel, Short Fiction, Poetry, or Genre.
3. Write blog posts that deal with the work of fiction you've posted. Perhaps give your inspiration for the piece, the theme, the symbolism, the characterization, etc.
4. Use really great eye-catching graphic images to illustrate your fiction.
5. Market yourself in the same professional way you are trying to market your work - with great graphic images, interesting profile, insights, etc.
6. Proofread relentlessly.
Take advantage of the free blogging platforms because less overhead means more profit.