Question

how is a solar eclipse caused?

Answer 1

When the moon comes in between the Sun & the Earth and cast it's shadow on the Earth that phase is known as Solar Eclipse.
It is usually not preferable to look at it with naked eyes as it might take our visibility away.

Answer 2

When the moon comes between Earth and sun, the shadow of the moon falls on the Earth which causes a solar eclipse..

Here are some images :-