You mouse cursor has four selection modes. Its default mode is Clip select, which allows you to click and drag clips within and between tracks. The precision with which you can move clips back and forward in time is determined by snapping. To deactivate or change snapping, click the View menu and select Snapping to choose the resolution you want to use when moving clips; you can move clips by beats, quarter notes, sixteenth notes, and so on, or none to deactivate snapping.