Can you explain why these different types of eclipses occur?
To understand these differences, let's investigate how light from the Sun is blocked by the Earth. Because the Sun and the Earth are not simply point masses, the shadow that is obtained isn't cleanly delineated (Why? Hint—would there still be a penumbra if the Sun were smaller than the Earth?). The regions of space in which all of the Sun's light are blocked by Earth is known as the umbra. If the Moon passes completely through the umbra, then we will obtain a total lunar eclipse. The view of the Moon would be completely blocked.
There will be regions of space in which some — but not all — of the Sun's light will be blocked by the Earth. This area is known as the penumbra. If the Sun, Earth, and Moon are not completely aligned, and the Moon touches but does not pass completely through the umbra, then we will obtain a partial lunar eclipse. A part of the Moon would be black, as if matter were actually missing.
If the Sun, Earth, and Moon are further misaligned so that the Moon passes through the penumbra but not the umbra, then we will only experience a penumbral eclipse! The diffuse outer shadow of Earth will fall on the Moon's surface, leading to a darkening but not a complete blockage.