“brought them to Joshua and...poured them out before Yahweh.” The articles were brought to Joshua, who took them before the ark of God so Yahweh could see them.
“poured them out.” This is the standard vocabulary for the pouring out of the drink offering. Here, the stolen articles were poured out on the ground as if they were a drink offering to Yahweh. The English is somewhat awkward, but the Hebrew text is trying to make a point that should not be lost in the English translation. Jericho had been an offering to Yahweh, it had been devoted, and this was part of the spoils of Jericho.