There are four kinds of ships that you can produce for your fleets. You can click the images and links to check more details.
The ships can equip a weapon, an armor, an engine and three kinds of special devices at the same time.
There are four kinds of weapons; beam, missile fighter, cannon. They have a special engage protocol (check the Battle page for further details.)
Armors increase the durability, engines increase the invasion ability. So use them well to cover the weakness of your fleets.
Special devices can increase a lot of things, like weapon accuracy, avoidance rate and so on. However, you can't make your fleet equip the same device twice or more, so you should combine different kinds of devices.
If you need a method to enhance your fleets regardless of the combinations, check the Formation page.