Article: The saddle is the part of your guitar that's below the pickups, on the opposite side of your headstock. If you've never adjusted the guitar's intonation, your saddle might be more difficult to move. Before you adjust the position of the saddle, loosen the strings so that you don't create unnecessary tension on the strings which could cause them to snap. If the saddle is being difficult, you can wiggle it back and forth with your fingers until it moves. If your note is flat, you'll want to move the saddle up towards the headstock. Loosen the screw a quarter turn to sharpen your note. You may have to do this several times before the string on the 12th fret is correct. Use a screwdriver to tighten the screw on the saddle if the string that you're playing is sharp. This will move the saddle away from the headstock and will flatten the note on the 12th fret. Once you've made adjustments with your screwdriver, you can re-tune your strings. Test the note on the 12th fret and take note of whether you corrected the problem. If you turned the screw too far, your string might be off the correct tuning. If this is the case, then loosen the string again and adjust the screw more until the string plays in tune, on the 12th fret.

What is a summary?
Loosen the strings to give the saddle freedom of movement. Loosen the screw on the saddle if your string is flat. Tighten the saddle screw if the note is sharp. Retune your strings.