My understanding of modes is as follows.
I always forget the names and the exact theory behind but it still works.
Play an open Low E Drone.
Now play a D Major scale over it and try and land on the E notes.
That's Dorian. That's it.
Even though it's a D Major Scale you don't have to start or end with a D note.
But since it's an E Drone try also landing on the B and G notes, within your D Major scale.
Play any D Major scale shape/pattern all over neck.
If you play an A Drone, then play a G Major scale over it, that's Dorian too.
D Drone---play a C Major Scale. Etc.
Mixolydian---Play an E Drone, play an A Major scale over it, again land the notes you think sound best (I think's it's Mixo.)
---Play an A Drone, play a D Major Scale over it.
Moving along to the other modes, follow this video, it's really easy and makes sense.
http://www.youtube.com/watch?v=JKbPIGnqt80
Don't worry too much over the theory yet, start with this video
and the theory will start to make sense later down the road and will also become valuable.