Some weapons give their wielders a Strength bonus in close combat or when shooting. This is clearly indicated in the weapon's profile. For example, a halberd has a +1 Strength bonus, so if used in close combat by a warrior with a Strength of 3, any hits caused are resolved with a Strength of 4. Note that this Strength bonus only applies when the warrior is using the weapon - his Strength characteristic remains unchanged for other purposes.
Some Strength bonuses only apply in the first turn of a combat. This reflects the fact that the weapons are especially cumbersome or exhausting to use. This restriction is indicated in the weapon's description.
Some Strength bonuses only apply in the first turn of a combat and only if the user has charged that turn. These are weapons that rely upon the impact of the charge to pierce the foe. This restriction is indicated in the weapon's description.