The 5-6-7-8's: WooHoo
WooHoo is a run of notes that walks up and down a scale known as the Mixolidian Mode which is an odd name but only one note different from Major. It is then moved, or ‘Transposed’ around to match chord changes. Very Common in early rock.
Letters above the tab are the chords behind the riff. Notice there's 12 of them, it's called 12 Bar Blues.
Vital tip: the frets used are from second to fifth inclusive; that's a span of 4 frets and you have 4 fingers. Set up your hand with a reach from 2nd to 5th fret before you play & crawl the notes like a spider, not hop-scotch.
A A A A D D
E [-----------------|----------------|----------------
B [-----------------|----------------|----------------
G [-----------------|----------------|----2-4-5-4-2---
D [-----2-4-5-4-2---|----2-4-5-4-2---|0-4-----------4-
A [-0-4-----------4-|0-4-----------4-|----------------
E [-----------------|----------------|----------------
A A E D A A
E [-----------------|----------------|----------------
B [-----------------|----------------|----------------
G [-----------------|----------------|----------------
D [-----2-4-5-4-2---|2-4-5-4-2-0-----|----2-4-5-4-2---
A [-0-4-----------4-|------------4-2-|0-4-----------4-
E [-----------------|----------------|----------------