There are three ingredients in a triad. The root, the third, and the fifth. The root and the fifth will stay the same for both minor and major triads. The only thing that changes, is the third. In the case of a major triad, the third will come directly from the major scale. If we use "A" as our example, we have "A", "C#" (C sharp), and "E". To play an A minor triad, we just make the major third one and a half steps lower, and we get "A", "C", and "E". This basic difference is what defines a major, verses minor triad.