The statement closing date for your credit card is the date that the current billing cycle ends. The next cycle starts the next day. On the closing date is a statement balance. The balance is carry-over unpaid from the last cycle, plus interest, new charges in the billing cycle, minus payments and credits. There may be pending charges or credits that are still in process. The billing cycle determines any interest due, or if you have been paying the full statement balances before the due date, generally interest is waived. Cash advances are usually charged interest from the day of the cash advance.
It's important to understand how revolving charge cards work, and all of the terms used.