I've just recently started playing D&D 4e through the Red Box, and I am confused about how to fill in the power cards. So, take Nimbus of Holy Shielding for instance. I understand the Target and Hit components as well as the effect, but my question is about the Attack component. It reads: _ (Wisdom) vs Will. Does the mean what ever my Wisdom score is, without the modifier, is compared to the Will score of the enemy? So, then would I not even have to roll a d20 to see if it works?
It means you roll your d20, add your Wisdom modifier, and compare it to the enemy's Will. You don't just compare your Wisdom score to their Will - that isn't what's used here.
On Scores and Multipliers
If you have 20 Wisdom, that's your wisdom score. 20 wisdom gives you a wisdom modifier of +5. The wisdom score is not used in the roll at all. Aside from being used to calculate the modifier, ability scores are very rarely used directly. If anything ever actually uses your wisdom score, not just the modifier, it will explicitly say so with the words "Wisdom score" or something similar.
On Attack lines
In an Attack line, the "X vs Y" is, in general, an ability (Strength, Intelligence, etc) vs a defence (AC, Will, Fortitude or Reflex). You always roll the d20, add the specified ability's modifier to the roll's result, and compare it to the specified defence. If the result is equal to or higher than the defence, the attack succeeds.
I'm sure somewhere your Red Box's books should explain how to read a power card and explain the nature of all lines that will show up on one, though not possessing the Red Box myself, I couldn't tell you where or whether it does. The regular (non-Red Box) Player's Handbook does at the very least, and I imagine the Rules Compendium does too.
I just addressed this issue with one of my groups. Hopefully what I told them should help you out as well.
Attacks and Damage
Whenever you attack an enemy, there are two parts to it.
Attack - Determines whether or not you hit the enemy. Attack will ALWAYS be determined by rolling a d20 and adding any attack modifiers. Attack will always target a certain defense which you should read whenever you make the attack. If you roll a 13 and have a modifier of +4 and the skill is targeting reflex, you would say something along the lines of "17 versus reflex". There is another important issue with attacking. If you roll a natural 1 (1 on the d20) you just experienced a critical miss. No matter how high your modifier (even if it's above the enemy's defense) you cannot hit them. Conversely, if you roll a natural 20 (20 on the d20), you just scored a critical hit. You are guaranteed to hit the opponent and deal the maximum amount of damage possible for that attack.
Damage - After you get a higher number than the enemy's defense with an attack you roll for damage. Damage is stated on the card (usually through dice rolls + a modifier). Some attacks may include 1[W] (or 2/3/4 [W]) as part of their damage. This means your weapon damage times the number before it. So if an attack deals 1d8 + DEX and you have a dexterity modifier of +3 and you roll a 6 you will deal 6+3=9 damage.
These are the cards you find on your character sheet. They give you all the information you need to use a power.
Action Type - States what type of action the power is. Most likely this will be a standard action for an attack, but always read it to make sure.
Attack Modifier - This is what you add to your dice roll to determine if your attack hits. It is also displayed at the bottom of the card for each weapon you have equipped, I would highly recommend using the number next to your weapon because it will always account for any bonuses your weapon may have.
Targeted Defense/ Versus Defense - This is the defense your attack will target. Always let the DM know what this is when you make your attack. Damage - This is the damage your attack will deal. Once again, it is also displayed next to the weapons you have equipped and it is recommended you use this number as it will account for any bonuses your weapon may have UNLESS you weapon deals more damage in certain situations such as when an enemy has no allies adjacent to it, these bonuses must be remembered and added after the fact.
Range - This is how far your target may be from you. This will most likely say "Melee 1" (one square away from you) or "Ranged X" X being the number of squares away that you may fire. It may also include the words "Close burst X", "Area Burst X" or "(Close) Blast X". All of these denote areas of effect (powers effecting more than one square) and you can read what each of these terms mean on pages 271-2 of the Players Handbook 1. Target - What can be targeted by the power. Creature means absolutely any creature, friend or foe. Take this into account when using area of effect spells as they may harm your allies as well.
Power Type - This will most likely say "At-Will", "Encounter", or "Daily". This lets you know how often you are allowed to use the power. At-Will may be cast whenever, Encounters recharge after a short rest, and Daily Powers are recharged after an extended rest. This area may also say "Utility Power" in which case there should be a box elsewhere on the card that has all three types written down and a checkmark next to the type that the ability is.
Effects - Many attacks have more effects than just damage. These usually appear in the area labeled Hit, although they may also have their own separate section on the card. When you hit with an attack these effects also take place.