This card's effect has 2 timing, [When Digivolving] and [When Attacking]. What does that mean?
This effect will activate in both timing [When Digivolving] and [When Attacking]. When you digivolving into this Digimon, it will activate as a [When Digivolving] effect, and for the following turns when this Digimon attacks, it will then activate again as a [When Attacking] effect.
This card has "you may to . Then, " If I do not do , am I still allowed to do ?
No, you cannot. If you do not do you cannot do the rest of the effect. (See more in Effect Structure#Optional and Mandatory Effects