Campaign Missions
These are the main missions you will be sent on in Campaign mode, they tend to be the most difficult missions to complete but will earn you the best rewards. Although you can attempt to complete these missions regardless of what level you are at it is advised that you wait until you have met the requirments. Most of these missions will come from Slade in The Hub.
Side Missions
Side missions can be picked up from most of the vendors at The Hub, they take roughly the same length of time to complete as the Campaign missions and will earn you decent rewards. The Campaign and Side missions will both give you gear and weapons.
Operations
Although you will not be able to pick up gear playing the missions in Operations they are the best way to increase your XP and your fame. Operations are split into six sections and they can be picked up from vendors all around The Hub.
Intel Run:
You need to search for a Torment mainframe, clear out the resistance, then hack the date.
Infestation:
These missions see you destroying breeder pods. To complete the mission you need to destroy them all.
Assault:
These missions involve wiping out all of the Torment forces in one or more locations.
Hunt:
On these missions you need to hunt down and kill a specific elite Torment enemy.
Jamming:
These missions require shutting down a warp engine and will usually involve shutting down one or more forcefields.
Kill Zone:
This is a wave-based battle where you and some marines who are backing you up are confronted with different enemy waves.
HUB Missions
These missions are picked up from the various vendors in the Hub and either invlove earning a set number of XP, a set amount of Fame, or selling pieces of armour or weapons at the armoury and the weapon shop.
Fame Hunter Missions
These missions are picked up from Hakim in The HUB and tend to be similar to HUB missions except they will be more specific and a lot harder to complete. You can increase your Fame substantially completing them.