Your Inbox contains any topics that require your attention.
The topics will stay there until you have taken one of the following actions:
For more information about commenting in topics, click here
In Cyans there are no "read"/"unread" messages. Instead, topics stay in your Inbox until you take an explicit action. In most cases, adding a comment, or closing the topic makes sense.
But sometimes you are participating in a topic that does not require your action (i.e. "FYI", or "I'll get back to this later..." messages from others). In those cases you can Acknowledge the topic by clicking the Checkmark button. This also moves the topic from your Inbox into your Open box.