Weapon Proficiency
Most classes grant proficiency with basic melee weapons and small arms. Combat-oriented classes, such as solarian and soldier, grant proficiency with more categories of weapons, as noted in each class’s Weapon Proficiency section. All characters are proficient with any natural weapons they might have, such as a claw or bite attack. If you use a weapon with which you are not proficient, you take a –4 penalty to attack rolls with that weapon, and the DC for any saving throws against that weapon’s special effects likewise takes a –4 penalty.
Source
Core Rulebook pg. 243