Next to Dates, you can select the See calendar of lowest fares option to find the lowest fares available within a 30 day period.
Enter a value of zero within the Duration (nights) field for same-day travel. Enter a range with a dash if your plans are flexible, such as 7-9 for a trip of about a week.
For weekend trips, enter 2-3.
After you search, you'll see a calendar showing the lowest price for trips beginning on the day you specified. Choose a departure day from the calendar to get a list of itinerary options.