The workbox is a tool within Sitecore for easily viewing the status of items within workflows which you have access to.
The Workbox is the default notification mechanism for workflow within Sitecore. It allows the easy sorting and actioning of tasks assigned to each user. In the screenshot, the view is filtered to only show the Sample Workflow. The user has the ability to view the work, note changes and move items (or all items) to subsequent steps. Also, each view has the ability to output to RSS.