Slayer reward points are only accessed after the Smoking Kills quest. The rewards that can be bought with these points include Slayer experience, a Slayer ring, the ability to combine all Slayer headgear into one item, the Slayer helmet, and even the ability to prevent players from being assigned a specific task forever.
Since getting good tasks worth keeping isn't guaranteed, it is suggested that players get their first four kills on the Slayer master Mazchna, and then get any other kills from there on higher masters like Duradel.
After getting 5 or more tasks in a row, Slayer masters will hand out points when players finish their tasks. The number of points varies as the difficulty of the Slayer master increases.
After earning enough points, players will be able to buy rewards with earned points.
You get the slayer reward points in Runescape once you finish a challenge assigned to you by any slayer master like Mazchna and Vannaka. You have to complete the smoking kills quest for the opportunity to be unlocked.