Hi Anya, Welcome to the Forums,
It’s an important question. Currently there is no way to create or import skins into UEFN.
The idea seems at-odds with the current business model. (of Selling skins and cosmetics) But at the same time, it’s hard to imagine a metaverse without this flexibility.
However, it is possible to import animations and play those on your characters, so I’d say that’s the best place to get started.
I imagine in the not-too-distant future you’ll be able to use custom skins in UEFN experiences that you create. (And in the far future, a vibrant marketplace of skins that can be used anywhere)