WOW! You got some kind of teacher, he should be explaining this all to you before you started practicing these scales. Maybe not the theory behind it, but you should at least know what a key is and what that has to do with scales. Ok, well a key is the home base of a scale. Like if you play a C major scale, C is your root or key. It's the first note and last note you play when practicing your scales. When you hear someone say a song is written in the key of C, they mean the song uses and is written in the scale of C major. A mode is taking the C major scale again (or any scale), but starting on another note other than C (it‘s root). Like if you start on D, your playing the D dorian mode. [u]The pattern of the scale stays the same, you just start and end on a different note[/u]. Now some theory about how scales are constructed so you can better understand them and use them. Take the C major scale. It is called the major scale cause every note from C is a major interval (or perfect). Here's a look at intervals from C.

C - C#(Db) - minor second
C - D - major second
C - D#(Eb) - minor third
C - E - major third
C - F - perfect 4th
C - F#(Gb) - tri-tone
C - G - perfect fifth
C - G#(Ab) - minor sixth
C - A - major sixth
C - A#(Bb) - minor seventh
C - B - major seventh

Now take all the notes in the C major scale (C, D, E, F, G, A, B) and they are all major intervals. This is very important for harmonic analysis (don't worry sounds more complicated than it is).

Another note, a minor scale is different. Actually the minor scale is a mode of the major scale. Play the C major scale but start on A, and you have the minor scale. Also called A Aeolian mode.

Now for melodic analysis. You just look at the interval pattern of notes ascending and descending in the scale. This is recognized as either whole-steps or half-steps. Take the C major scale again. Starting with C...

C - D - whole step
D - E - whole step
E - F - half step
F - G - whole step
G - A - whole step
A - B - whole step
B - C - half step

All major scales are made of this pattern. (wwhwwwh) You'll see that a lot. Guitar players prefer it cause it's easy to see on the fret board. A whole step is 2 frets away, and a half step is the next fret (or 1 fret away).

Last is the chord analysis of the major scale, in this case C again. Each scale has a chordal structure that exists within it. This extremely easy to figure out, what you do is with each note in the scale (I'm going to use C to illustrate in a second.) and skip a note, and the skip another note. Here’s an example so you can see.

C major scale: C, D, E, F, G, A, B
As I said. C, skip D, E, skip F, G.
You end up with: C, E, G

Which is a C major chord.

Chord's are formulated by using harmonic analysis. Take the first layout I wrote, starting from C to E, and then E to G. You end up with a major third (C-E) and a minor third (E-G). A major chord.

Here are the chords.
Major: major third, minor third
minor: minor third, major third
diminished: minor third, minor third
augmented: major third, major third.

Do this with all the notes in the C major scale and you end up with the chordal structure for the key of C major.

C major / D minor / E minor / F major / G major / A minor / B diminished.

Sometimes you will see it as: I, ii, iii, IV, V, vi, viio.
Here's the translation: Capital Roman numeral is a major chord, small roman numeral is a minor chord, small roman numeral with a small "o" beside it is diminished, and a Capital roman numeral with a "+" beside it is augmented. I (i) is always the root.

That's pretty much everything you need to know how to understand scales and modes. Just apply it to a the new scales you learn and you've got the basic understanding on that scale from front to back. More information can be found by using the search option on this page. Good Luck!