Or, if you know where you are, simply ring the bell when your stop approaches. Sometimes drivers will announce stops. Some public buses have cords and others have button strips for requesting a stop. Don't wait 'til the last second. This transfer is valid for two more rides in the next two hours.
Buses accept dollar bills and all change.
At the train stations there are vending machines where you can get a transit card for the dollar amount that you put in. Take the Blue Line from O'Hare to Washington. You are blocks away from the Hilton. You are blocks away from the Hilton. Walk south on Jefferson past Jackson to the Blue Line subway.