There is some novelty in a spaceship that has no shield, but no captain is really foolish enough to risk a battle without one, or several. Not only do they offer sustained damage mitigation, they also save quite literally astronomical amounts of credits in repair costs.
A basic shield creates a circular bubble that stops incoming threats, converting their kinetic energy to an incandescent display of light and heat. More advanced shields can be projected over a specifec arc and distance, opening up tactical options for a talented captain.
The two most important attributes for a shield are the maximum capacity and recharge speed. It is up to the captain to decide which one to favor more, based on their combat approach. Other important aspects to pay note to are in no particular order: