Hi zed,
The ATR(Average True Range) indicator gives you the average range of a security in a specific period of time i.e. for example over the last 10 days the stock moved in a Rs.12 range every day on an average.
This information can be used in many ways for example it can be used to find out the rate of return and plan out your target achievements i.e. how much within what time period.... or the ATR could also be used to find out just how much does a stock swing either way in a day or in a minute or in a week etc, you could then use this information to place a stop loss which would be 2*ATR or 3*ATR etc.