Once you know how to attack, the next thing you have to think about is avoiding enemy attacks. That's where the shield button comes in handy.
Shielding against attacks is a top priority. If you don't take any hits, you can't be beat! However, the more attacks your shield takes, the smaller it gets.But more important than guarding is dodging. You just tap the Control Stick in a direction while holding the shield button.
If you can do these moves, your enemies will have a hard time landing their attacks. And they make you momentarily invincible, so using them proactively is OK.