If the Moon blocks out the Sun completely, we call it a total solar eclipse. If it only blocks out a section of the Sun, then it's a partial solar eclipse. Finally, because the Moon's orbit around the earth is not perfectly circular, sometimes it will be perfectly aligned with the Sun, but still the solar disk will poke out around the edges. Then we have an annular solar eclipse. Because the Sun is so bright, unless it is totally eclipsed, it will be too bright to see with your eye.
Total eclipses are very rare, totally spectacular, and only last a couple of minutes.
If you can, take a trip to see one. About twice a year, the Moon will cross the ecliptic at a location exactly opposite that of the Sun. When this happens, the Moon will get in the Earth's shadow. This is a lunar eclipse. Although the Moon is being eclipsed, it does not disappear completely.