Press Esc to view the Pause Menu and click "Journal". On the left side of the screen, there are two tabs for viewing missions: "Missions" for main story missions, and "Side Missions" for optional and miscellaneous missions.
Viewing Main Missions[ | ]
In the Journal, select "Missions".
Under "Open Missions", you will see main story missions that are currently active. Under "Completed Missions", you will see any main story missions you have already completed. Click on a mission to learn more about it.
Viewing Side Missions[ | ]
In the Journal, select "Side Missions".
Under "Open Missions", you will see optional missions that are currently active. These can be completed at any time and are not critical to the main story. Under "Completed Missions", you will see any optional missions you have already completed. Click on a mission to learn more about it.