Spaces are areas of the HailTo app dedicated to the projects you have been invited to. Each project has its own individual space.
If you've been invited to multiple spaces inside HailTo, you can switch between them at any time by tapping on the HailTo logo in the top left, or by swiping right from the left edge of your screen.
You can now view all the spaces you have been invited to, and switch between them by tapping on icon of the space you wish to access.