Spring tides occur when Earth, Moon and Sun are aligned in a straight line and the tidal bulges display constructive interference, producing very high, high tides and very low, low tides.
Spring tides coincide with the new and full moon.
Neap tides occur when the Earth, Moon and Sun are aligned forming a right angle and tidal bulges displaying destructive interference, producing low high tides and high low tides. Neap tides coincide with the first and last quarter moon. Earth on its axis and the Moon in its orbit both revolve eastward and this causes the tides to occur 50 minutes later each day.