IM in the first level where its objective 05 and i need to "enter the transport depot and board one of the carts".i kill everything i think im supposed to and when i go into the one cave and kill the people in there i get my "waypoint finder"and it shows im suppose to go through an opening where a pipe is going through,how do i continue?? any help would be great thanks in advance

Find the path up to the level above you. Jump onto the structure opposite and then make your way onto the pipes and follow them to the hole in the wall.