If it's a CREDIT card, yes it will begin accruing interest immediately upon use. Yes, you can pay the balance off online. Keeping in mind the time difference, allow a day for the transaction to post in the USA, maybe two days. For security reasons, be careful about going into your accounts online on a computer not your own. And don't do banking over a wireless network.

If your card is a DEBIT/ATM card, no interest, just the exchange rate and whatever fee Chase levies (I have one of these though haven't used it here in China for a while, I think it was a flat $2.00 per withdrawal).