In a total solar eclipse, the moon appears to completely cover the sun. Even though the sun is much larger than the moon, because the moon is much closer to Earth it appears to be the same size as the sun which makes solar eclipses possible. During a total solar eclipse the moon is passing between the sun and the Earth, and the moon's shadow gets cast on the Earth.
Solar eclipses can be total, partial, annular or hybrid. Which type a person might see depends on their location on Earth relative to the moon and sun and the moon's location in its orbit relative to the Earth. If the moon passes directly in front of the sun and the shadow reaches the Earth's surface, it is a total eclipse. If the moon passes in front of the sun but doesn't cover it completely, it is a partial eclipse. If the moon is at a point in its orbit in which it is too far away for the darkest part of its shadow, called the umbra, to reach the Earth's surface, it is in annular eclipse (think of placing a penny on a nickel with the moon being the penny and the sun being the nickel). If the umbra just barely reaches the Earth's surface, it is a called a hybrid eclipse.