Question one: Earth style is a technique that enables the user to control the earth surrounding him, and can be used to attack or defend the user, this includes all types of earth (Rock, Dirt, and mud.)
Question two: Earth's strengths are against water because Earth structures spread out the movement of the water slowing it down and making the attack less effective, but is weak against lightning because lightning can travel easily through earth and break it apart.
Question Three: Jirōbō, Kakashi Hatake, The Third Hokage.
Question Four: Earth Style : Earth Dome, Earth Style Wall, Earth Style: Tearing Earth Turning Palm.