The selling process is quite simple. Just go to their site, register yourself as a seller, list your product in their marketplace and when the customer buys your product, you will get a notification to make the shipping arrangements. Some sites allow you to ship the product to the customers directly while some take care of it themselves. Once that is done, the sites will deduct their fee and transfer the rest the amount to your bank account.

As for your query on hefty commissions, look at it this way. All you have to do is upload pictures of your origami on their site. The marketing, advertising, distribution (for most of the sites), etc. of your business is taken care by them. So in that case, giving a certain percentage of your sale will still be beneficial for you. The volume of business that these sites can get you is much higher if you restrict yourself to the local market. This is my suggestion. Rest is your call. I'm sure you are wise enough to decide what's good for your business and what's not.

A simpler solution here is to go online. You don't have to take much efforts in finding a store that can partner with you or invest in a studio to sell your origami models. My wife too makes origami models and she sold quite a few items online just by sitting at home. It is the simplest and most cost-effective way and besides, with online platforms such as Etsy, Origami USA, Michaels, etc. you will be reaching out to people from all across the world that would not be possible from a local store. Your customer bandwidth increases without any marketing needed. I mean, if this isn't a great deal for a beginner, I don't know what is.