To see whether any hits are scored, roll a D6 for each model fighting. If you have more than 1 Attack with your troops then roll a D6 for each Attack. For example, ten Elves have 1 Attack each so roll 10 dice, but four Ogres have 3 Attacks each so roll 12 dice!
The dice roll needed to score a hit on your enemy depends upon the relative Weapon Skills of the attacker and his foe. Compare the Weapon Skill of the attacker with the Weapon Skill of the model it is trying to hit and consult the To Hit chart to find the minimum D6 score needed to hit.
If you look at the chart, you will see that normally models hit an enemy on a 4+, but if the warrior's Weapon Skill is greater than that of his enemy, he will hit on a dice roll of 3+. In the rare case when an enemy's Weapon Skill is more than double that of the attacker, a 5+ is required for a successful hit. Sometimes modifiers apply to these rolls, but normally an unmodified roll of 6 always hits and an unmodified 1 always misses.