The sixth interval seems to be a a breakthrough concept for many players, for some it might be hard to remember a time before you knew a couple little sixth phrases. If your new to the idea, its more simple than you think. Starting on C, let’s count six notes in the major scale: C, D, E, F, G, A. That means C and A are a sixth apart, its that simple. You might think recognizing two notes that are a sixth apart might be harder on the guitar but that’s not too tough either. You see sixths on the guitar are characterized by skipping a string. In all of these licks if I jump from one string to another and skip one in-between, that’s probably a sixth.