Triad is a group of 3 notes around which all chords are formed. A major triad is the 1st, 3rd, and 5th notes of the scale. A minor triad is the 1st, 3rd flattened, and 5th notes of the scale. Those are just a couple examples.
Hi, I'm Peter
By fretting the notes?
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just figure out the key and which triads to use(major,minor etc.) and as elven said just fret them

Quote by xdan666x
so how do i play them in a solo for example
You don't really use chords as a soloing thing. You could play triad arpeggios though.

Click basics and use the arpeggio finder to find some triad arpeggios as well as more complex ones.