Power Chords, Barre Chords & the Blues
This is the rock level. Power chords — usually three strings (root, 5th, octave) — are no theory, all attitude; they're the whole sound of Weezer's "Buddy Holly." Then the 12-bar blues, built from a two-string shuffle and written out in full. Finally barre chords (full F, Bm): your index finger becomes a movable nut so you can play any chord, in any key, anywhere on the neck.
Concepts
A power chord is usually three strings — the root, its 5th, and the octave. No major or minor; it fits anywhere. (Drop the octave for a thinner two-string version.)
The shuffle is a different move: hold the root and rock ONE string between the 5th and 6th. That alternating pattern is the engine of the 12-bar blues.
The 12-bar blues in E: E E E E / A A E E / B A E B — and that last bar is a B turnaround that pulls you back to the top.
A barre chord is an open chord shape with your index finger acting as a movable nut. Slide it for any key.
Graduation
Play the full 12-bar blues in E with the shuffle, all the way through the B turnaround in bar 12.