There are a number of ways to share a workspace, and the visibility of your workspace can be changed via the workspace settings page.
The workspace can be only accessed by signed in users who you have given access to using role-based access.
This is the default for new workspaces.
The workspace is public on the web, and can be accessed by anybody without signing in.
Public workspace URLs are easily guessable, so use this feature with caution.
A sharing link can also be enabled/disabled for individual workspaces, which is a simple way to provide people with a read-only view of the diagrams and documentation in a workspace.
Although the link uses a random token (a GUID), which is incredibly unlikely to be guessed, please do remember that, like sharing links in other online applications, anybody who has access to your link has (read-only) access to your workspace.