Gravity pulls the Oceans, the Seas, and large Lakes. This results in water being pulled towards the same area – creating a high end and also a low end on the Earth. When the Sun and the Moon are aligned this effect is even more prominent, and results in an exceptionally high tide known as the Spring tide when the water can rise especially fast. When the Moon and the Sun are at right angles to the Earth the effect is not so strong – those smaller tides are called neap tides.
Our sun is 27 million times larger than our moon. Based on its mass, the sun’s gravitational attraction to the Earth is more than 177 times greater than that of the moon to the Earth. If tidal forces were based solely on comparative masses, the sun should have a tide-generating force that is 27 million times greater than that of the moon. However, the sun is 390 times further from the Earth than is the moon. Thus, its tide-generating force is reduced by 3903, or about 59 million times less than the moon. Because of these conditions, the sun’s tide-generating force is about half that of the moon (Thurman, H.V., 1994).
A horizontal movement of water often accompanies the rising and falling of the tide. This is called the tidal current. The incoming tide along the coast and into the bays and estuaries is called a flood current; the outgoing tide is called an ebb current. The strongest flood and ebb currents usually occur before or near the time of the high and low tides. The weakest currents occur between the flood and ebb currents and are called slack tides. In the open ocean tidal currents are relatively weak. Near estuary entrances, narrow straits and inlets, the speed of tidal currents can reach up to several kilometres per hour (Ross, D.A., 1995).
Oceanography Course: http://www.iupui.edu/~g115/mod12/lecture01.html
Tide predictions: http://www.ukho.gov.uk/Easytide/easytide/SelectPort.aspx
What are tides: https://oceanservice.noaa.gov/education/tutorial_tides/tides01_intro.html