What does smashing mean?

Answer 1

It's a type of move that typically does more damage and has more launch power than other moves. It's among the best ways to knock another player off the screen.

To perform a smash you press a direction and attack at the same time. It takes careful timing so you may need to practice it a little.

Or if you use a game cube controller you can use the yellow c-stick to perform a weaker version of a smash.