Like a minor scale, a mode comes directly from a major scale. You just start and end your scale on a different note in that scale.
Here's a regular C major scale:
Remember that this scale has a certain combination of steps that makes it sound like a major scale - in this case 2 2 1 2 2 2 1. We covered this in the lesson on major scales. This scale, our basic major scale, is also called the Ionian mode.
Our next mode is the Dorian mode. We're still in the key of C major, but this time instead of starting on C and going to C we're going to start on D and go to D:
Notice how it doesn't even sound like a major scale anymore? It's the same notes, but we're not playing the same sequence of steps this time, so we get a delicious minor scale called the Dorian mode.
Take an as a scale by itself, the steps in this scale would be 2 1 2 2 2 1 2.
Here's the chart with our chords in a major key. I've added the modes that start on each note:
C E G - Major - I - Ionian
D F A - Minor - ii - Dorian
E G B - Minor - iii - Phrygian
F A C - Major - IV - Lydian
G B D - Major - V - Mixolydian
A C E - Minor - vi - Aeolian
B D F - Diminished - vii° - Locrian
Try playing all these modes separately. For instance, to play a Lydian mode you would start on F and go to F using the same C major scale notes. Each of these scales has a different sound because we're making a different pattern of steps every time!
You can actually create chord progressions that "bring out" a particular modal sound. Some songs are "modal" meaning that they emphasize a particular mode.
Let's say I want to make a progression that brings out that nice Dorian minor sound. The chord that matches the scale is the ii chord, or Dm in our key of C. So here's my "Dorian" progression:
ii V ii V
Try it out - you may recognize it as a Pink Floyd song, or maybe it sounds like a particular Santana song, but when you solo to this using the key of C, you don't get the standard major scale sound - it's more of a Dorian sound because we're emphasizing the ii chord.
Try writing some modal chord progressions in different keys and see what kind of great sounds you can coax out of a major scale.