The Opening Range (OR) is defined in terms of time and price.
The time element is simply the first X number of minutes in the trading day. The number of minutes used to define the Opening Range is your decision as a trader. The most commonly used OR is 5 min and 30 min OR.
The price component of the OR is the day’s trading range at the end of the OR time period. This means that the 30-minute OR is defined as the stock’s high and low for the day at 10:00 AM. The OR is not the opening price. In fact, the opening price is not a factor in calculating the OR. For example, if Amazon, Inc were to open at $46.49 and then sell off to $46.06 at 9:45 AM and then reverse and rally to $46.66 at 9:55 AM and then proceed to sell off into the middle of the day’s range until sometime after 10:00 AM, its 30-minute OR would be the day’s range at 10:00 AM or $46.06 – $46.66. This is because during the 30-minute OR period $46.06 and $46.66 were Amazon’s low and high, respectively.
A typical OR trading is to place a buy stop above a wide open range bar or a sell stop below a wide open range bar, better there're some small consolidation bars after the wide range bar so that you can have a low risk entry (as you can set a very tight stop loss). The following 2 sample images are from http://traderjamie.blogspot.com