Corvettes are the bread and butter of any fleet. While large capital ships are difficult to build and maintain, a fleet of corvettes can be kept in working condition without much effort. The absence of a hangar on these fleet ships mean that they expend a lot less energy maintaining a forcefield to hold the atmosphere. Corvettes alone don't carry nearly as much firepower or armor as a capital ship, but an intact fleet of corvettes will nearly double the firepower available to a team.
Flak corvettes provide excellent fire support against tactical ships and incoming missiles. Flak is a surprisingly potent weapon in space, and these corvettes will tear up the hull of any fighter or bomber within close range. The only ship capable of putting up with flak is the gunship, with its heavily armoured hull. Bombers need to keep their distance from these ships and bomb them from afar.
Gunboats usually spearhead a fleet, and provide long range support. They fire powerful torpedoes which can penetrate the shields of any capital ship and deal a fatal payload directly to the hull. While all corvettes have offensive weaponry to be used against the enemy capital ship, the gunboat is the one that will be felt the most, especially when the shields are taken down.
Missile corvettes work similarly to flak corvettes in repelling tactical ships, but do so at a much longer range. Their pegasus missile turrets detect and shoot down enemy fighters and gunships up to a kilometer away. The fast-firing, slow-turning pegasus missile struggles however when a tactical ship gets in close.
A capital ship surrounded by corvettes is practically impossible to board, the powerful guns prevent any kind of large scale boarding attempt. This is why corvettes are priority targets at the start of any battle. In order to successfully board, the corvettes must first be taken care of. Fleet command is typically quick to respond to this type of action however, warping in new corvettes as quickly as possible to defend vulnerable installations and capital ships. Losing a few corvettes is pennies compared to losing an entire capital ship and it's crew.