How does stacking work in Uno and what are the rules for using this feature during gameplay?

In Uno, stacking allows a player to play a 2 or 4 card on top of another 2 or 4 card, forcing the next player to draw more cards. The rules for stacking are that the next player can also play a 2 or 4 card to pass the penalty to the following player, and this can continue until a player cannot or chooses not to stack.