A workspace is a physical location you can work from. It can be a single desk or many desks.
The way you book it is similar to how you book a conference room in Outlook. Workspaces have a capacity and minimum booking duration requirement that are set by your IT admin. For example, if a workspace has 10 desks, then only 10 people can book that workspace and the 11th person will receive an automatic decline.
After you book the workspace, you'll initially see an entry in your calendar but that doesn't mean the booking is confirmed. You will receive an email with the status of the booking.