You can download the software — > By Visiting https://www.blender.org/download/
And when you put your thinking Cap, this is a pretty solid and applicable idea.
The idea is simple. You need to get your hands on a 3d printer by buying it!
And then you need to start designing stuff in blender. Watch a few tuttorials that teach you the basics.
Now, create a product, a new kind of spoon, or a rocking chair. It can be anything that you want. I would suggest.. That you create a small product that you can easily print on your printer.
And then test the product by creating replicas and clones. And deposit them or give them to a resource who will keep your 3d printed product and sell it for you, especially in the market.
Now, when the units get sold? Go directly to the mold creator, create a mold and start manufacturing.