A workspace is where all the work that you do in Toggl Plan happens. All Teams and Plans, tasks and milestones as well as users, settings and - important to note - billing plan are a part of the workspace.
One user can have multiple workspaces with different users and billing plans. At the moment, it's not possible to copy a workspace - all of them have to be set up manually.
Click on the workspace name at the top of the sidebar to open a drop-down menu with all the workspaces you're part of and to easily switch workspaces.
Go to Settings -> My profile -> Workspaces to see all the workspaces you're part of as well as any pending invitations to new workspaces. You can also rename and delete all your workspaces here.
Global settings, or the settings that affect all of your workspace (meaning, they are not only visible to the person making the change) are workspace names, everything billing-related, users and their roles..