alright, so my education on modes has just started rather recently, and as retarded as it sounds im already confused. so basically i am to believe that the A Dorian mode actually relates to the key signature of g major...therefore, when would you actually use it, in a song in G or a song in A? help would be appreciated, im so lost
if you play it in G, you're just using the G major scale, because it has the exact same notes as the G major scale. If you play it in A, you're using the real A dorian scale that will be unique in that situation.
Alright, you need to back up a step.

Yes you are right that A Dorian and G Ionian contain the same notes, but they are not used the same way. Each mode has with it it's own set of chords created by the harmonization of that mode.

For example, G Ionian chords: G, Am, Bm, C, D, Em, F#b5, G
A Dorian, Am, Bm, C, D, Em, F#b5, G, Am

Now, yes they are the same chords but their function in the key has changed and thus different progressions would arise from using these two scales.

Now, the usefulness of modes comes more with playing the scale over certain chords. For instance. A Gmaj7 chord contains G B D F#, thus while playing over this chord you can play any scale containing these notes (and even some that don't, that's a subject for another time) So you could play, G Ionian or G Lydian over it. Both scales have those notes in them, the only difference is the #4. But that #4 could be exactly what your looking for.

Also keep in mind, that you can play horizontally as well, meaning playing the scale of the same key of the song over the entire song. It really comes down to what the song deserves. Playing the key of G Ionian over the entire duration of a G-C-D-C progression would come out a lot different than if you played vertically meaning that you play G maj over the G chord, C major over the C chord, D major over the D chord and so on and so forth.

I hope this gives you some ideas, and a better understanding of modes. Keep working on them, I have found that modes help me a great deal in learning songs by ear and also taking what I hear in my head and getting them out onto the fretboard. Good luck.
Quote by Rockdaparty44
You would use A Dorian in the key of G since they both use the same 7 notes A B C D E F# G

No, you would use G major in the key of G.

If you use the notes of G major over a tonal centre of A then you have A Dorian.
Actually called Mark!

Quote by TNfootballfan62
People with a duck for their avatar always give good advice.

...it's a seagull

Quote by Dave_Mc
i wanna see a clip of a recto buying some groceries.

Just a side note, when I have seen modal music written out there might be three sharps (as in Key of A major) with a note accompanying saying something like "Key signature indicates E Mixolydian" or just "E Mixolydian". Of course you could work it out by looking at the chord relationships to figure out which one is acting as the tonic.