Yeah - for a new player understanding this, it might be easier to read this as
Attack: Strength vs AC, using main weapon
Target: one creature
Damage: 1[W]
Effect: Make a Secondary Attack using your off-hand weapon
Secondary Attack: Strength vs AC, using off-hand weapon
Secondary Target: one creature not targeted by the first attack
Secondary Damage: 1[w]
Where upper-case W is main weapon damage, and lower-case w is offhand weapon damage.
Note that there is a
huge difference in the way I've phrased it, and this is why the game designers haven't phrased it this way:
In the power as originally written, both attacks are simultaneous. You declare the targets concurrently, you roll to-hit concurrently, and you roll damage concurrently. Therefore, an Immediate Reaction triggered by the main weapon's attack doesn't have any chance of stopping the off-hand-weapon's attack.
The way I've written it above -
for example purposes only - would change that, making it so that an Immediate Reaction triggered by the main weapon's attack to conceivably affect or stop the off-hand-weapon's attack.
Hope that's helped to clarify things - if those last two paragraphs are confusing you, re-read the original power, compare it to the way I've got the example worded, and re-read the PHB (Players Handbook) section on Immediate Reactions until it makes sense!
