How do I reserve a hotel room online?

I know how to make reservations for one, but do they actually charge anything to the credit card that you put on the account before you physically get to the hotel?? I want to make reservations now, but I wont have the credit card I actually want to pay for it with until Saturday, ... If you have the CC number book the room on-line, then when you check in make sure you have the card and ID in hand, they will need it for check in. Or you can pay cash when you check in. ...