First, you pick your team; I'll use D&D terminology for roles if that is okay.
Managers are leaders, the clerics or warlords of your team. Receptionists are strikers, rogues or rangers with ranged and cone attacks. IT Guys are controllers, of sorts, as they are lousy in melee, but have area of effect attacks. Salesmen are defenders who fight up close and hamper enemies.
I have won a few times. You can have the game pick your team for you, but I always lose that way. Instead, I send the secretarial pool after my opponents. Just like D&D, strikers are the best killers. Unlike D&D, no one has to survive for the next battle. I have taken a team of six receptionists and mopped the floor with the opponents; between their ranged attack (stapler, range 4 squares), cone attack ("1000 Paper Cuts"), and high damage melee ("Cream & Sugar") they are pretty unstoppable. I'll add a salesman sometimes, as they can limit enemy movement with their "harassment" attack. Managers (like in real life) are rarely effective, and the IT Guy is only really good when mobbed.
To win the game, you either need to capture eight cubicles, or kill off the enemy team. You can overtake enemy cubicles that are unoccupied, and get a bonus to attack based on how many cubicles you have captured. There are power-ups on the board that typically buff the one who grabs it, or the team as a whole. There is also a PvP "multiplayer" mode where you can play other intenet players, either having the system find you a remote player, or you can create a private game to play a friend. To do this one of you will "create private game" and send your opponent the passcode generated. Your opponent will select "join private game" and enter the passcode provided.
It is a lot of fun, though I am lousy at strategy games. Below is Adult Swim's commercial for the game to give you a better feel.