I too found it a little perplexing. Here's how to do it:
3) Edit the Details and Table sections.
4) When you get to the armies, click 'Define',
not 'Import'
5) Now, don't click 'Import', 'Army Builder', etc., like you probably think that you should in order to import your army from the army builder. Instead, look to the bottom of the first fieldset. Hey, there's a Template dropdown! Ignore all the other fields and pick your template from that dropdown. Now the other army fields get filled in. But wait, you're not done yet.
6) In the lower fieldset ('Units'), click 'Unit from Template'. At the bottom, click 'Select All', then 'OK', then 'OK' again. Now your army has been imported.
It's counter-intuitive, but not difficult once you figure out that the first thing that you want to do is the last field, and that Import is not what you use to import the army file that you created.