Can anyone lead me to, and/or give me advice on webshop building software?

Initially for fun (read trying), later maybe serious, I want to wrestle a bit with building (first) and running a webshop.
I searched a bit but it wasn’t that clear to me, the info I read, so I turn to you: Do you know of any simple and cheap (preferably free) software to do this?
I want to start with doing it for myself, with virtual products, and if I get the hang of it, I might want to use it for real.
Thank you in advance!