Guitar players answer..?

As you already know, open chords are generally played on the first few frets. Barre chords allow you to move those same chords to other places on the neck by "barring" with your first finger, basically the same thing you would do with a capo, but you can't quickly move a capo from fret to fret during a song like you can your finger. So take the E open chord you already know. Now instead of making that chord on the first two frets, try moving it down a couple frets, it will now sound completely wrong. Now hold down all of the strings (barre) with your first finger and then make the E open chord with your other 3 fingers in front of that barre. You have just made your first barre chord. Power chords are just what they sound like, powerful. With power chords you are usually just playing the last (fattest) 2 or 3 strings which gives a very fat and powerful sound, think AC/DC for instance. The basic definition of a scale is this: "A scale is the notes you use to get from one note to that same note 1 octave higher." A scale is also something to build a lead or riff off of. For instance Zakk Wylde is known for using the minor pentatonic scale in many of his leads.Hope this helps.