It depends on which type of leaf, but I'll try to show you a simple one. I found this picture, I hope it's useful.
A major triad can be created with 3 notes, by starting with a note, like “C” then adding a note a major 3rd higher, “E” which is four half-steps, then on top of that, adding a minor third (3 half steps up), above that G. C-E-G
A major third can start on any notes, using the same formula of major third and a minor third
D-F#-A, Bb-D-F
Eb-G-Bb.....