So I asked around on this forum:
http://odd74.proboards.com/index.cgi?board=eptIt seems that a lot of people house rule this because it can seem a bit vague.
It looks like the high stats give you bonuses to attack (Hit Dice), and that bonuses to Damage Dice are a bonus to the actual roll of the dice like standard D&D. Interestingly a high Con doesn't give you any additional Hit Points, or at least my interpretation of the rules gives me that impression.
So if you had +2 Hit Dice, you would roll a D20 and add 2 to the attack roll.
If you had +2 Damage Dice you would roll the damage listed for your weapon plus any additional damage dice (D6s) for being a higher level vs a lower level target, and then add +2 to the total.
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