Missions are requested by the users of the forum therefore you do not get assigned missions by mods or admins. Therefore if you wish to go on a mission you must ask them if give you a mission for you can do. When asking to do a mission you must tell the admin or mod if you wish him to create the scenario of the mission for you or ask if you can use your mission pending it approved. Either way the mod/admin will start the scenario for you and guide the mission along throwing enemies at you and obstacles for you to over come. Depending on how well you handle it they will judge the outcome of those scenario and what happens. REMEMBER if you do something stupid they can kill off your character in C, B, A and S ranked missions. At the end they will judge weather or not the mission was completed.
The mod/admin will edit the title of the mission to reflect the failure or competed nature of it and give out points for the complete mission.