When you play scale chords you have to know the major scale. The pattern to find the major scale is.
Whole step, whole step, half step, whole step, whole step, whole step, half step. You start on C to find the Cmajor scale. This will give you.
C, D, E, F, G, A, B, C
When you play scale chords you play up the scale. Thats how you know wether to play a major or minor chord. When you play the first chord Cmajor you keep your fingers in that mold and play up the scale. The Cmajor chord is CEG. Notice the notes all have a note in between the notes in the C major scale.
C and E has a D in between. E and G has a F in between. Play up the scale using the next note up for each finger and you will come out with the chords.
Cmajor, Dminor, Eminor, Fmajor, Gmajor, Aminor, Bdim.
Actually you should get a basic understanding of how to form the major chords first. Then you will understand why you play minor, diminished, suspended, and augmented chords.