>Roll 2 dice + all modifiers that apply. Add together all dice of the same value and take the highest value (so if you rolled 1,3,3,4,4,4,6 then it's actually, 1,(3+3),(4+4+4),6- meaning that the value is 12.)
>Opponent rolls defense
>Subtract defense from attack. If the result is 0 or less, attack misses. If it is above 0, it hits.
>If it hits, multiply the (attack-defense) roll from earlier by (1+damage mods). That's your damage.
>If you deal half your opponent's max HP or more in damage, they lose their next turn.
And that's how you basic attack.
Power Attacks are similar except they have a flat amount of damage that can only be increased via the extra damage mod