Ocean currents
Ocean currents are large, persistent movements of water, driven mainly by wind patterns, the Earth's rotation, and differences in water temperature/density. Warm currents (flowing from the tropics towards the poles) raise the temperature of coastal areas they pass; cold currents (flowing from polar regions towards the equator) cool coastal areas and can reduce rainfall by limiting evaporation.
Example 1: Explain why a coastal region next to a warm ocean current tends to have a milder climate than a similar coastal region next to a cold current.
A warm current transfers heat from the ocean water to the air above it, warming the coastal region's climate and often increasing rainfall (more evaporation from the warmer water). A cold current has the opposite effect, cooling the coastal air and often reducing rainfall.
Tides
Tides are the regular rise and fall of sea level, caused mainly by the gravitational pull of the moon, with a smaller contribution from the sun. Most coastlines experience two high tides and two low tides roughly every 24 hours as the Earth rotates.
Ocean relief features
The continental shelf is the shallow, gently sloping seabed nearest a continent, where most marine life and fishing activity is concentrated. Beyond it, the continental slope drops more steeply down to the abyssal plain -- the vast, relatively flat deep ocean floor.