Hi Luisa,
A solar eclipse happens when the moon comes between the Earth and Sun and blocks out part or all for the light from the Sun's disk. At least a partial solar eclipse happens somewhere on Earth every year.

Here are some web pages about eclipses:
http://www.exploratorium.edu/eclipse/why.html
http://www.dustbunny.com/...onders/solareclipse/
http://www.mreclipse.com/Special/SEprimer.html

Terry