A traid is simple, just a chord made out of three notes seperated by a third. If you know what a third is on a guitar, a triad is simple, just root, third, fifth.
With a guitar it's simple to do intervals, each fret is one semitone, and in between strings if either 5 or 4 semitones, so for a minor third just count out 3 semitones, or for a major count out 4 semitones. If you use the perfect fifth, you get either a nimor or a major chord depending on which third you used, and you can use dimished fifth(basically two minor thirds together, or 6 semitones) along with a minor third for a diminished chord, or the augmented fifth(8 semitones above the root) with the major third for an augmented chord.
This is probably more musical theory than you needed though
Check this out for more information:
http://www.zentao.com/guitar/theory/organize2.html