A solar eclipse occurs when the the moon's shadow blocks out sun disk.  This happens when the the moon comes between the earth and the sun.  The moon must be in the new moon phase and the  orbit of the sun, moon, and earth must be exactly in line, usually the moon orbits the earth at an angle above or below the line of the sun and earth and so you would not have a solar eclipse every month.  A lunar eclipse occurs when the earth's shadow falls on the moon.  This happens when the earth comes between the moon and sun in its orbit.  Again the orbits must be line up exactly.  The moon must be in the full phase.  Lunar eclipses last longer the solar eclipses and are visible to anyone have night time.  Solar eclipses occur in a narrow path so they are not visible to everyone during the day, only those in the path of the eclipse.

During a solar eclipse, the sun is eclipsed, or blocked from view. This occurs because the moon passes between the sun and the earth. Solar eclipses can be partial, total, or annular, a form of eclipse where the central disk of the sun is blocked but the outer edge, or corona, stays in view.

During a lunar eclipse, the moon is eclipsed, or blocked from view. This happens when the earth passes between the sun and the moon, and casts a shadow on the moon. The only time this can occur is during the full moon phase, when the sun, earth, and moon are in a straight line relative to one another.

Neither type of eclipse happens terribly often because the orbits of the earth and moon are elliptical rather than circular, and the orbit of the moon sits at an angle relative to the orbit of the earth around the sun. Since an eclipse only occurs when the alignment is perfect, we only have them once in a while.