There are 5 unique codex entries in the Game Rules section on Ord Mantell. 1 is accessible to all players regardless of class or faction and 4 are class specific.
Energy is obtained from speaking with Viidu during "Security Breach" mission.
Codex type: Game Rules | Faction: Republic | Class: Smuggler
Associated Achievement: None
Energy Cells is obtained from speaking with Needles during "Mannett Point" mission.
Codex type: Game Rules | Faction: Republic | Class: Trooper
Associated Achievement: None
Item Modifications is obtained from from interacting a Clickable Plaque with during "Item Modifications" mission.
Codex type: Game Rules | Faction: Both | Class: All
Associated Achievement: None
Smuggler is obtained from speaking with Wentell Pron during "Legitimate Buisness" mission.
Codex type: Game Rules | Faction: Republic | Class: Smuggler
Associated Achievement: None
Trooper is obtained from speaking with Lieutenant Forris during "Best of the Best" mission.
Codex type: Game Rules | Faction: Republic | Class: Trooper
Associated Achievement: None