Quote from Page 18 "which models fight:
....If a warrior is touching more than one enemy, he can
choose which to attack. If he has more than 1 Attack,
he can divide them in any way the player wishes, so
long as he makes this clear before rolling to hit."
If you read the next paragraph on page 19 it becomes even clearer
"hitting the enemy
To determine whether hits are scored, roll
a D6 for each model fighting. If a model has
more than 1 Attack roll a D6 for each attack."
Wounding is dealt with in a later paragraph.A good guideline when trying to understand any rules is looking at the sequence in which they are appearing in the rulebook, generally this indicates the order in which they are done in the game.
So basically you announce all models you want to attack and with how many attacks you attack each of them. After that all dice rolls for hitting the enemy have to be done BEFORE you roll to wound, together this prevents you from taking advantage of "early hits" to attack other models.