How does it start? I mean, what units do you start with, and are there ways to get more?
In Co-Op, you each start with different units and you can't resupply them except at specific parts of the mission. In Skirmish, you each start with units and they respawn. You can get more by capturing facilities. In Assault, you each start with units and they respawn.
What units you get is dependent on the map. Here's a video of an Assault level--Not the best quality, but the best I could find, anyhow.
There's definitely some strategy there, but I think success is based more on your swiftness in giving orders, threat assessment/elimination, and knowing when to leave units behind or send them forward. That sort of thing. Either way, it's 15 bucks on eBay, which in my opinion is 35 dollars cheaper than I should have paid for it.