Combat Achievements
Combat Achievements on Sarim RSPS award perk points, which you spend on unlocking and upgrading player perks. Open the list in-game with ::cas.
How they fit progression
Perk points buy player-perk unlocks and upgrades. All six active perk slots are open from the start, so points never buy slots. Your lifetime perk points keep counting after you spend them.
Some Combat Achievements also unlock content. Completing Unrequired Antifire, for example, opens Echo Cerberus. Each Echo boss page lists its unlock task.
See also Sarim Achievements, Perks Menu and the first-day guide.