Typical fighters roll 2d10. Men at arms and other cautious types roll 3d6. For more complex rules, see the rules section. Each time a character gains a level of force, they also gain three points of WIL of which they must spend at least two. WIL is traded off when skills are improved, rune connections strengthened, etc.
Force is expended when magic items are bonded, familiars obtained, etc.
Magic items typically have a force level. If the character's force is not equal to the force of the magic item, the item will have a negative result instead of a positive one. FOR is added to WIL v. WIL contests, but otherwise affects things only if there is a magic focus available. Weapons and items can be crafted that do not require matching force. The most obvious example in mythology would be the One Ring of the Lord of the Rings.