From the Ground Guide:
Car parking at the stadium is for permit holders only. However, there are a number of pay & display car parks located around the town centre. Otherwise, there is some street parking available around the area of the Millmoor ground, which is around a 15 minute walk away from the visitors turnstiles. There is a multi-storey car park located next to the Interchange Bus Station which costs £2.80 for four hours, or other council Pay and Display car parks in the area costing around £2 for four hours.
Away fans are normally housed in the Mears Stand at one end of the stadium, where around 2,500 supporters can be accommodated. The stadium has electronic turnstiles meaning that you have to insert your ticket into a reader to gain admission. Cash is not accepted at the turnstiles and tickets for the away section can be purchased from the dedicated away ticket office at the back of the Morrison Stand.