An account on Air is a personal identifier that is attached to your email address. Air accounts can join or create a workspace. When you create an Air account you are automatically prompted to create a new workspace.
To join an existing workspace:
Have a workspace admin select "Invite Members" from the dropdown menu next to the workspace name
Enter in the email associated with the new member
The new member will then get an email invitation sent to confirm
To create a workspace:
Click the "+" sign in the blue ribbon running down the left of your current workspace
Name your new workspaces