The galaxy overview is accessed from the Main UI. The fleets and planets tabs provide you with a detailed overview of your empire, making it easy to quickly find and manage any of your empire's units.
This view shows all your empire's fleets as well as those of other players that are currently within scanner range. Filtering by ship type will show only fleets with at least one ship of that class within a fleet.
For each fleet, you can see the cumulative stats and resources, which can be further broken down on a ship by ship basis by clicking the arrow to expand the ship list for that fleet.
All planets within scanner range are listed here and can be filtered by ownership. Where possible, full details of the planet and its colony are available.
Clicking the eye icon will zoom you to the planet to manage it.