First go to a project page. From the project page click the project settings cog.

From the projects settings page click the “Statuses” link in the sidebar.

From this page you can add custom statuses and define what type of status it is (open, resolved, or closed). This allows you to be more granular with your statuses while still maintaining a flexible and simple workflow.  

In the example below, we’ve created a few custom statuses, like “In Progress” and “In Review”, which are organized under the “Open” Status Type.

Be sure to watch this quick tutorial video for a step-by-step walkthrough.