You just have to send an email to the host (you'll find his address on the top of the thread), and attach your solution's file..
You'll find it in the Armadillo Run folder --> Levels (usually C:\Program files\Armadillo Run\Levels)
It will look like this:
ARFC_B_LXX_BRIDGE.The_name_you_gave_to_your_solution
The name of the solution should be:
[DollarsRemaining]-[YourForumName]-[SolutionName]
Example:
9999-Andreas-Light
So you should submit something like:
ARFC_B_LXX_BRIDGE.9999-Andreas-Light
You can rename it saving the level in AR, or change the name in the "Levels" folder...