I don't know how use this spell yet

이 주문 어따 써야할지 모르겠음 아직도

The key to this spell is that you can use Dash as a bonus action instead of using your action for that, so it is available for other options. In the turn when you cast the spell, as it is cast in the bonus action, you can also dash. 

So since the turn you cast the spell, that turn included, and for 10 minutes (assuming your concentration is not broken) you can dash as a bonus action instead of using your action. 

The wording is not entirely clear. Can you dash again once as a bonus action sometime during the 10 minute duration or every bonus action during the 10 minute duration?

Huge difference in value of spell. The 2014 spell was clearly the latter but the wording has now changed,

Quote from CreepingButtercup >>

The wording is not entirely clear. Can you dash again once as a bonus action sometime during the 10 minute duration or every bonus action during the 10 minute duration?

Huge difference in value of spell. The 2014 spell was clearly the latter but the wording has now changed,

The behavior of the spell hasn't really changed from the 2014 version. You take the Dash action immediately as part of casting the spell, and for the rest of the duration of the spell, you can take the Dash action as a bonus action.

The change in wording does mean that if you have some feature that allows you to take a bonus action on someone else's turn, you can now use that to take the Dash action, whereas technically the 2014 version didn't allow that. I'm not aware of any feature that lets you do that, but there it is.

Thanks

“Until the spell ends”

Since it doesn’t end when you Dash, it is still in effect for every turn for 10 minutes: 101 Dashes max.

101 from the spell itself. You can still Dash as an action on all of those turns too, so really the limit is 202 Dashes absent any additional assistance.