The apparent magnitude is the brightness of a star seen from the Earth.
The Absolute magnitude is the apparent magnitude of a celestial body.
The apparent magnitude is the measure of how bright the star is as viewed on Earth. Basically, the brighter the object seems to be on earth, the lower the value of its magnitude. The scale is based on the numbers 1-6. 1 being the brightest and 6 being the least bright.
Absolute magnitude is the apparent magnitude of a celestial body at a standard luminosity distance away from Earth. This is the calculation in which it does not take into account any thing that might skew the distance.
For the second part of the question. Absolute magnitudes are calculated so that it holds everything constant. If this is so it would be much greater than compared to what we can see (apparent). Therefore that is one of the reasons why there is such a difference between the apparent and absolute magnitudes of 'some stars.'