The Ionian Mode (the definitive major scale) is the mode built on the first degree of the Major scale. In C, CDEFGABC. The characteristic pitch (what makes it unique) is the natural 4th degree.
The Dorian Mode is the mode built on the second degree of the Major scale. In C, DEFGABC. It is a minor scale because the third is lowered a half-step from what it would be as a major, and so is the seventh degree. The characteristic pitch is the natural 6th degree because this scale would otherwise be the same as natural minor.
The Phrygian Mode is the mode built on the third degree of the Major scale. In C, EFGABCDE. This is also a minor scale because third, sixth, and seventh are lowered a half step from the major, and characteristic pitch is the b2 because this scale would otherwise be the same as natural minor.
The Lydian Mode is the mode built on the fourth degree of the Major scale. In C, FGABCDEF. The characteristic pitch is the #4 because this scale would otherwise be the same as the Ionian mode or Major scale.
The Mixolydian Mode is the mode built on the fifth degree of he Major scale. In C, GABCDEFG. characteristic pitch is the b7 because this scale would otherwise be the same as major.
The Aeolian Mode is the mode built on the sixth degree. It is the same as the natural minor scale, the characteristic pitch is the b6 because that is what makes it natural minor.
The Locrian Mode is the built on the seventh degree of the Major scale. In C, BCDEFGAB. This is a minor scale because the third (as well as 2, 6, and 7 are lowered a half step from the major). The characteristic pitch is the b5 because this scale would otherwise be the same as Phrygian.
Click here for a printable handout on The Modes of Major.