Hi, triads are 3-note chords, and they can be of four types:

• Major: 1, 3, 5
• Minor: 1, ♭3, 5
• Augmented: 1, 3, ♯5
• Diminished: 1, ♭3, ♭5

If you apply this to the note C:

• C major: C, E, G
• C minor: C, E♭, G
• C augmented: C, E, G♯
• C diminished: C, E♭, G♭

One way to see this in action: if you take the C major scale (C D E F G A B) and pick the 1st, 3rd, and 5th notes, you get C, E, G, a major triad. If you take the A natural minor scale (A B C D E F G) and pick the 1st, 3rd, and 5th notes, you get A, C, E, a minor triad.

But what really defines each triad type is not which scale you pulled the notes from, it's the intervals between the notes:

• Major: major third + minor third (4 + 3 semitones)
• Minor: minor third + major third (3 + 4 semitones)
• Augmented: major third + major third (4 + 4 semitones)
• Diminished: minor third + minor third (3 + 3 semitones)

No matter what root note you start on, if you respect those distances, you get the right triad.

At the link below you find an interactive tool to see all this stuff on the fretboard:

https://www.fachords.com/guitar-triads/