if you not active your new master card, what will happen?

Depending on the issuing institution, it may become activated automatically or you can be reported to the credit bureau. Being approved for a credit card is a serious compromise, if you want to be cool I would suggest you to keep it (but not uset it, unless its really necessary) for at least 1 year. Most of the time institutions are not charging fees during the first year which would be a safer time to cancel the card.

If the account has an annual fee, that will show up on your statement. If you don't activate the card, the company will eventually close the account in about 7 months or so.

nothing...just sits there.

The account is open whether or not you activate the card. Activation is just a security feature. If you don't want the account, you have to close it.

Nothing is charged until you activate the card..case closed.

If the account has not been activated then they can't charge you anything so don't activate it and no charges, fees or interest will take place.

No, if you don't activate your card, you are not charged anything but the annual fee if there was one. You may want to consider in sending it back if you don't want to activate it.
If you have an interest rate, the annual fee can become higher and higher with interest acruing. Best to send it back.