I was troubled by modes for the longest time! but they are really not that difficult: The Dorian Mode is the second position/mode of any scale. Ex: D Dorian is the second mode of C. Phrygian's are the third mode in any scale. E Phrygian is the third mode of C. Lydian's are the fourth mode. F Lydian is the fourth mode of C. Mixolydian's are the fifth mode of any scale. G Mixolydian is the fifth mode of C. Aeolian's- the sixth mode of any scale. A Aeolian is the 6th mode of C. Locrian's- the 7th mode of any scale. B Locrian is the 7th mode of C. The eighth mode would bring you back to the first, which is called Ionian.
Just to clarify, these are all scales! Basically they are different variations of the same scale. The patterns remain the same no matter what key you are playing in. However they do change depending on whether you are playing Major or Minor, for example, if you are playing C Major, the Mixolydian scale, which would be G Mixolydian, would have a different shape than if you were to be playing C Minor.
Just an FYI, all of the scales in any key have the same notes. They are simply played at different octaves, therefore having different sounds.