To convert items in the cube, click the transmute button, visible only when the cube is open. The cube can be held in your inventory or your town stash.
Dropping the cube will instantly move everything from the cube to your main inventory, with anything you lack space for dropping to the ground. To open the cube, right click on it, then click and drag to move items between the cube and your inventory. They will automatically be positioned within the cube, assuming there's enough free space for them to fit.
To use the Horadric Cube, simply drag and drop items on it.
