When does a lunar eclipse take place ? Does it occur on every full moon's night?

When the earth comes in between the sun and the moon, the earth casts its shadow on the moon and the part of the moon which lies within the umbra of earth, will not be visible from the earth. Thus, the lunar eclipse takes place.

No, lunar eclipse does not occur on every full moon's night because the Moon's orbit is slightly tilted with respect to Earth's orbit. Due to this tilt, the Sun, Earth, and Moon do not always line up perfectly in a straight line during every full moon.