Posts that have assignees will have an associated status. Assignees - and the entire post - can be open, resolved, or closed. You’ll see the live status of the task in your feed denoted by color - orange for open, green for resolved and grey for closed. The icons of posts with no assignees will be blue.
You'll also see the project-wide counts by status in your Project Pulse on the web, helping you see how your company is tracking on tasks.
Assignees can access the post and update their own status to "Resolved" when they've completed the task. The post creator can then mark the assignee "Closed" once they've okayed the work.