Modes can be confusing, but once you figure out the number system formulas, they become WAY easier. I like to think of ANY scale as a scale with a certain set of alterations from the major scale. In this case, Dorian is just a major scale, but with a flat 3 and a flat 7. Once I figured out this approach, it made SO much more sense than saying "Dorian is the 2nd mode of the major scale." Like, that's obviously true but to me, thinking about the alterations to the major scale is far easier to thin