ToME: the Tales of Maj'Eyal

Can someone explain the effect of each and provide some specifics? Would like to understand from a base damage perspective how to interpret each of these values.
I'm assuming physical power is a 1:1 damage bonus?
Not sure about size category, all I can figure out is the bigger you are the harder it is to hit a halfling

Physical power just adds to the Power value on your weapon for all damage calculations. Remember power is applied before multipliers so it can be worth a lot more than it might seem at first.

The simplified attack damage works something like:
(Power - Armor)*Multipliers

Multipliers are stuff like Weapon Mastery and Talent damage.

As far as I know, size category doesn't have a direct impact on the game, so only specific talents are affect. At the moment only Halflings and Brawlers should even think about this.

There's a few talents that check for size category such as shadow simulacrum and temporal clone. Otherwise what Dervis mentioned is right.