two answers
an inverted chord is a chord which has another note than the root as the lowest note... Take a D major, played at the second fret if you let the fourth string vibrate and be the lowest, you have a d major. If you play an F#, 6 string second fret, and let it be the root, you now have an inverted chord, where the notes have been inverted from their original order.
As for the second answer, the long note you say is controlled feedback which you need to have volume and distortion to get. Sometimes, we make the guitar strings vibrate by facing the amp. This is the same principle, except this time, the note stays the same, and doesn't go in an harmonic one octave or a fifth higher, you might want to hear gary moore blues alive on parisienne walkways for a 20 seconds hold!!!