See the main article on attack here.
Attack allows you to wield better and more powerful weapons. Attack also allows you to make successful hits more often.
See the main article on strength here.
Strength enables you to hit higher in melee. This complements Attack as together they make it easier to hit higher and more often.
See the main article on defence here.
Defence is useful in combat of any kind to reduce the amount of damage an attack hits on you, the higher the level the less you will be hit. Also, Defence allows you to wear stronger armours.