The answer to this question depends on what you want. If you want a very quick store that you can set up, with ability for checkout, then I think signing up for a website like Etsy or ArtFire would be the quickest and most efficient option.
Here is my Etsy shop, so you can see how it sort of looks like an online store. You can add a banner to it. In February, I interviewed John Jacobs, the CEO of ArtFire.com, so check out that interview here if you'd like to know more about ArtFire.
If you want to have a free place where you can show your art, but you don't necessarily need the ability for customers to checkout - you just want an online showcase where can direct people to see your art, then ArtWanted would be a good place for you. It's free at the basic level, but you can only upload a certain number of images per month at the free level. You can upgrade to a paid account to be able to upload more images. Keep in mind that your username will be part of your web address (URL) on Artwanted, so keep it short, catchy, or your real name (if your name is easy for people to spell and remember!)
You can get free websites at Tripod, Homestead, Weebly, and GooglePages. Unless you upgrade to a paid account, you may have ads on your website pages. The last time I checked, GooglePages did not have ads in the pages, but surprisingly, my GooglePages site doesn't rank very well in Google! You can see what I did with it here. I found it pretty easy to work with. My own pencil portrait art website is hosted on Tripod. That doesn't mean that it's necessarily the best for me or for you. I've just had it there a long time, so I'll probably just leave it alone.
Of course, this only brushes the surface - there's so much more that goes into creating a website. But for someone who's a beginner and just needs a nudge in the right direction to create a website presence, I hope this will help you.
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