From Destinypedia, the Destiny wiki
At the beginning of this mission, you will first spawn in the Headlands, just like of it were a patrol mission. You are instructed to head right, towards the Citadel. There will be an arrow on your radar to indicate where you need to go. Once you reach the Citadel, you are instructed to fight through the Fallen and Vex who are at war with each other, culminating at the bottom of the Terminus. After you slay all the enemies, your Ghost scans the terminal and you will ride the column of energy upwards towards the Terminus and you will have to cross the chasm. Once you have done this, lots of Fallen will spawn where you arrive. Kill all of them and proceed forwards. You encounter two High Servitors and two gates, one on each side. Once Skolas spawns in, you can shoot and disable the gates from letting in any more Fallen. Once Skolas' health drops to around 5%, a Vestian ship appears and surrounds Skolas in a containment field. You are praised by both Mara Sov and Petra Venj and return to orbit soon after.