The dice bag shows all your dice, saved rolls, and sub-bags on the hotbar.
This hotbar scrolls horizontally.
To spawn a die, just click/tap it here and one new die of that type will be spawned.
Dice can also be spawned/removed by dragging them from/to the hotbar.
Rolling a saved expression works the same way, but existing dice will be cleared first.
At the far end of the hotbar is a "+" button, click/tap it to add a new dice bag, die, or saved roll expression.
To delete, clone, move or edit a die, bag, or saved roll expression - right-click/long-press on its icon and then select the corresponding button.