What causes a solar eclipse? How often do they occur?

Hint: Solar eclipse is a phenomenon which occurs when the sun, moon and the Earth are aligned one after the other. It is advised that we should not look at the solar eclipse directly. Solar eclipses are a completely natural phenomenon. When it occurs a certain region of Earth is covered in shadows for some minutes.

Complete answer:
Solar eclipses are phenomena which occurs when the sun, moon and the Earth are aligned one after the other. Since the moon is in between the sun and the Earth, it blocks the sunlight reaching the Earth.
In solar eclipse, the Earth is completely or partially overshadowed by the moon as it blocks the sunlight which reaches that part of the Earth.

There are two types of solar eclipse; a full solar eclipse and a partial solar eclipse.
In a full solar eclipse, the disk of the sun is completely covered by the moon, while in partial solar eclipse, the disk of the sun is partially covered by the moon.
Solar eclipses usually occur at the new moon.
The solar eclipses only last for a few minutes at any place. These are rare events as they can occur every 18 months but they only occur once in 360 to 410 years at the same place.
Therefore, the solar eclipses occur when the moon blocks the sunlight reaching the Earth. Solar eclipses are events and can occur once in more than a year.

Note:
Just like solar eclipse, lunar eclipse occurs when the moon gets overshadowed by the Earth. The moon reflects the light from the sun. It occurs on the night of a full moon. The solar eclipse occurs when the moon is closest to the elliptic plane which consists of the sun and the Earth.