The trolley is a quest item given to the player during the Garden of Tranquility quest by Queen Ellamaria. The player must use the trolley to transport two heavy statues from Falador and Lumbridge to her garden behind Varrock Palace. The first is by the crossroads just north of the White Knights' Castle in Falador. The second is on the south pillar of the archway into Lumbridge Castle.
To move a statue the player must use the trolley on it. The player will pull the statue onto the trolley and it can then be pushed by standing next to it and using the action menu. Other players can see the statue (or trolley only if the player has completed the quest or is moving the statue) being moved.
Once the quest is complete and the statues are in the garden; the player will lose the trolley and the two statues will no longer appear in the spot they once were leaving just plinths behind.