I assume you're referring to the special where zerra begins to speed up while charging an attack, it charges a kick that has high knockback as well as builds up your speed. You can hit the button again to cancel it early or let it fully charge until you see two little ice crystals floating around her, then you can input the move again to throw it out. Also if you want to cancel it or shift your momentum back to the stage you can jump and then hit the neutral special. If you need more of an explanation or to just see it, i can show it to you in game aswell

The charge attack is tricky, You need to juggle on and off stage due to the momentum but keep a certain amount not charged as you need your ice to give you momentum as it disables when the move is fully charged which is a problem because your momentum dictates how much damage is done. Remember canceling it keeps the charge across most stages if you go one side to the other it takes about 3/8th of the stage to get to max charge.

Using it without really caring about getting it to max charge is very forward and can be good in a lot of situations plus it can be a really good way to fling yourself back onto the stage you are high enough.