Shields are used for defense, for each ship there is a single spherical shield bubble that protects it from each direction and stop every weapon as long as there is enough charge.
Shields are not meant to replace armor but complement it. Their main purpose is to prevent laser sniping. They can stop bullets but are very weak against them especially HE and gauss.
Shields can be deployed or undeployed, and are recharged in each state but while deployed a part of the recharge power is used to maintain the shield bubble. There is also a energy cost to deploy that depends on the shield bubble volume.