The Scanner is located at the bottom center of your main screen.
You can use your Ship Scanner to discover usable salvage in the system you're in. The result varies, depending on if the system you're scanning in is occupied by one of the factions. For example, it's more likely that you will receive a Bajoran transmission when you scan in a system occupied by Bajorans. You also can find items, tied to the owner of the system.
Once you used your Ship Scanner, there is a cooldown period of 3 hours. If you are at least at VIP Level 2, you can speed up the timer by spending Dilithium. The amount depends on the time left.
When scanning, you can find various amounts of the following: Credits, Components (any rarity), Equipment (any rarity), Ship Schematics (1 to 10), Transmissions (usually one).
You can't acquire Crew members, Merits or Dilithium when scanning.