The army builder is a simple page for helping you plan your Warmachine armies. It doesn't check for all of the rule conditions (like field limits) so you will need a working knowledge of how armies are put together before using this utility.
To use it, simply choose a caster and his jacks to form the battlegroup, and then fill out the rest of your army with as many solos and units as you can fit. The numbers next to the units specify the size of the unit, the numbers next to the solos determine how many solos you are taking.
If you plan to build a large army with a lot of units or solos, or you're playing some crazy Cryx army with 20 bonejacks per caster, you will want to change the number of slots before you start work on the army because changing the number of slots will reset all of the fields.