Go to the check box

"Show me lowest coach-class fares for travel during the period:" and select it.

A series of fares will come up. Select one and it will give you calendars and you will select dates. It will eventually give you flights and times to choose (you can continue choosing "more flights" until you get the ones you want). Not good for complex routings but OK for non-stops and simple one connections otherwise you cannot get flights you might want.