Attack: 30/0/0

It means they have 30 beam attack, 0 missile attack, and 0 mass driver attack.  (For the defense stats, it's shields/point defense/armor, in that order.)

I don't remember exactly how to get there, but I believe if you click on a details button with the enemy ship selected an Intelligence Report window will come up that further elaborates on this.  You can also access it via right clicking a ship in the diplomacy/trade window.

The details for a ship can be accessed from the main window by clicking on the little icons after the ship name, or simply selecting it and pressing "d".  One icon will bring up the details for how the ship was designed, and the other will allow you to rename the ship.  If it's a fleet, you need to first click on a ship in the fleet's ship list, which will change the "Manage" button just over it to a "Details" button, which will bring up the design details.  You can do this for any ship, though your own ships will have quite a few command options available that won't be there for opponent ships.

  Luckily, ship details don't require any overall intelligence on the race in question.  I'd say it's because you can simply look and see what bits are sticking out on their hulls