Light ships are excellent scout and assassin ships, but are too small to carry heavy weapons. They have the lowest health and highest speed in the game.  Light ships rely on their quick movement to dodge attacks.

It is recommended that new players avoid using them for combat until they know how to fully take advantage of the unit's speed.  

Medium ships are often used for cheap and mobile combat or support ships. They also are commonly used as gatherers or miners.  With four components, it can be armed with any weapon in the game.  

A medium ship can fill any role, but will often struggle at trying to do multiple different things at once.

Heavy ships are usually built for direct combat and tend to stick with the main fleet.  They can carry a mix of weapons and defenses.

These are usually a good ship for beginners, since they can be strong in head to head combat while still moving at a decent speed.

These behemoths can be wield a massive amount of firepower or defense, but can rarely dodge attacks.  They make excellent artillery batteries, as they can use two large weapons and still have space for supporting upgrades.

Think carefully about how you position them in your fleet.  These ships won't be able to run from a fight, and you my find them getting left behind the rest of your ships if you aren't careful.