i read this article here about intonation and how to do it, i dont need to do it at the moment but for future reference, i have a prob. it says:
'choose astring and play the 12th fret harmonic' how do i play this?
'using a tuner tune the harmonic' how do i do this? how?
and finally
'play the 12th fret note and tune it using the tuner' how can i tune the 12th fret? do i just find what not it is and tune it to that? if the tuner only tunes like open notes of the strings?

thanks if u can clear these things up, dunno f i explained them right but anyhoo, do ur best, thanks again
you play the 12th fret harmonic (which is a natural harmonic) by just touching the string above the 12th fret (not pressing it down to the fretboard) and then you pick the string, after which you lift your finger of the string to let the harmonic ring out.
You tune it to the same pitch as the string is in (in fact the harmonic and the fretted 12th note are both an octave higher, but normally the tuner is able to do this without problems)
tune the string your intonating first. Tune it exact. Next, hit the 12th fret harmonic (lightly touch the string over the 12th fret-bar, then let go right after you pick, it'll leave a ringing note). Check if it's the same as the open string. if it's not, change the saddle position accordingly (the article tells you how). rinse, repeat.

If your tuner doesn't pick up the harmonic, get a new tuner :p
Quote by JorisBlack
^that's not how you intonate

it's the FRETTED note on the 12 fret (not the harmonic) that you compare with the harmonic or with the open string.

All three should match in the end either way.