When you login to virtual spaces and go to the staff site (house icon in top right corner), then go to Modules, create a module (or use an existing one), and create a slide.

It is possible to add new text or image blocks to a slide, but new blocks will always be appended at the end (which is fine) and they can't be rearranged afterwards. What we need is that a user can rearrange the order of the slide blocks. So after adding a new one at the end, they can put it as first or second or whatever block either by drag and drop or by changing the order in a different way.