At the moment the site is in Beta and as such does not offer any facility as an online marketplace or shared repository, but they will do in the next phase. This from their FAQs:
"When we come out of beta, … you will be able to choose to make your designs available for purchase by others. This feature — which will make Spoonflower into a marketplace for independent fabric designers — will probably take some time to evolve and grow in complexity. But displaying your designs, as well as selling them, will ALWAYS be under your control."