|The following is based on information from Fallout: Brotherhood of Steel.|
In the holding pen area, ghouls are keeping humans captive. You need to free these poor people. Not only is it the right thing to do, but each freed human is also worth experience points. Turn south, approach the huge crate and take out the pack of ghouls. One of them has the key to the pens.
There is another locked gate to the north. One of the nearby ghouls has the key, so mow them down until you find it. Continuing, more ghouls will open fire on you from the sides, so take them out. More humans are incarcerated to the west, but the key is on a ghoul to the east, by toxic puddles.
Return to the pens in the west and start freeing prisoners. The guards are well armed, so take them out before they can kill any humans.