Ship Pods are a certain kind of items. They can give bonuses on various properties of your ship, or give you new functionality.
Pods are crafted via engineering, or bought from the CE Store. Each ship has a fixed number of Pod Slots, you can put at most one pod in each slot. A captain also has a maximum on Pod Points; each pod costs a number of theses points, and a captain cannot exceed the pod point limit for equipped items. You an purchase a Pod Point Expander License for your captain via the CE Store.
You can equip and unequip your pods via the Pods loadout interface.