Choose a type of martial weapon. You understand how to use that type of martial weapon in Combat.
You make attack rolls with the selected weapon normally (without the non-proficient penalty).
Martial Weapon Proficiency
When using a weapon with which you are not proficient, you take a –4 penalty on attack rolls.
Barbarians, fighters, paladins, and rangers are proficient with all martial weapons. They need not select this feat.
You can gain Martial Weapon Proficiency multiple times. Each time you take the feat, it applies to a new type of weapon.