"Are you going ice skating tomorrow?"
Translation:Dych chi'n mynd i sglefrio iâ yfory?
'Mynd i' followed by another verb is about a future action.
Dych chi'n mynd i = Are you going to (do something)
In this case 'sglefrio iâ yfory' = ice skate tomorrow.
Put them together = 'dych chi'n mynd i sglefrio iâ yfory?'
Literally this is 'Are you going to ice skate tomorrow?'
Which is transposed to the above.