I'm reading up on the basics of segmental phonology and can't seem to wrap my head around it. So the normal association line indicated the connection between the tonal tier on top, and the segmental tier below. One vowel may carry more than one tone, leading to a contour tone. So what does the dashed association line mean exactly? It seems to be necessary to explain floating tones in some way, which happens when a vowel gets deleted but the tone remains and needs to be borne by an adjacent vowel.
Dashed lines in a rule means "insert this line", or, in a shorthand derivation, it means "this line was (just) inserted". In the example of oke okpa, the vowel /e/ deletes and you have a floating tone as a result, as the part after the arrow indicates. On the next line, that H is associated to the vowel [o] of the second word. The problem that you are having is that the book was not correctly typeset: the last image should look like this:
What happened is that in the printed version, the dashed line was attached to the first tone in the sequence, not the second tone.
In the case òké òkpá → òkôkpá, the initial L and final H of the sequence are unchanged, because only the vowel and tones involved in vowel deletion changes (the first vowel deletes, the two tones of the V+V sequence merge into a falling tone). The vertical undashed lines represent unchanged associations (that's what "undashed" means); the (angled) dashed lines are the ones changed and, as it happens, "angled" is there to remind you that the tone came from elsewhere (though the angle of a line is theoretically meaningless). So the only errors are the point of connection on the tone tier for the dashed lines (at least, I think those are the only errors). The 4 added examples are correct: they mean "L H becomes L Rise", "H L becomes H Fall", "H L becomes Fall L" and "L H becomes Rise H", depending on whether the first tone spreads to the right, or the second tone spreads to the left.