“Clear the area of Vex so you can access the scene.”
Time for a fight and a large one. The first wave is a lot of Goblins and some Harpies. Stay close to the Gate and start clearing them out. Use area attacks because the Vex are commonly clumped together at the start. Rocket Launchers can also work.
Head down the slope after you have cleared out the first wave. You will find the second is being teleported in after that. Most will appear on the landing just below you. Take them out much like the last group. They start grouped together but they will spread out.
There will be another group appearing to your left just nearby the stairs. You will find this wave of Vex has some Minotaurs in it.You are getting close to the end of this fight.
The final group appears in front of the gate itself. You will need to clear them out to get to the final part of the first part.