Karma points are an abstraction of alternative wealth, these may be gained directly over the course of adventure awarded by the DM and are numerically directly analogous to gold (many times other forms of wealth can be converted to Karma by making anonymous gifts to charity). Certain items cannot be safely given away (OoI can be used to convert some items to Karma and others may have to be Sequestered - Sequestering involves taking an item to some hidden hard to reach place often with a guardian assigned - this process will effectively convert the item to Karma, becoming this guardian may be a backstory for retiring a hero).
After all saving the village maiden isnt something less deserving of reward just because a King will reward you directly with gold.
Advanced Techniques Cost in Karma is as per a magic item in gold of the same level. (more mundane ones which cost similar to analogous weaponry or armor in karma)
Legendary Boons or Charisms and Martial Techniques have aspects in common with martial practices one of those elements is they have a price
The Price: Though they often lack the overtly physical and rare components seen with rituals those long term effects have an additional more symbolic price they are said to incur a debt of Charity or a Karmic Debt. In game terms this is tracked via Karma points. Abilities created via rites usually incur a blood price ie a cost in terms of Healing Surges or sometimes use of Second Wind akin to martial practices/heroic exertion.
Karmic Price is for simplicities sake measured in gold but is often gained and paid in heroic affirmation quests which lack recompence, direct anonymous gifting to charity granted to those without means to compensate meaningfully, as well as spirit quests where in very little is ultimately real and anything aquired evaporates and turns to dust is also common as is garnering Karma via service to community (including benign rulership) .
Titheing this is a practice that allows one to gain Karmic surfeit. It also may allow a gift to be aquired somewhat prior to its Karmic debt being paid . Breaking a vow of titheing can have impact on multiple gifts.
Fated returns/Blood coin is a very odd effect when a gift is lost due to breaking a binding oath you sometimes regain your 30 pieces of tainted silver in away that feels wrong.
Cumulative Karma - in certain circumstances it is necessary to rank two bloodlined individuals (for instances when determining who's land gift affect party nature skill - Current Karma and Cumulative Karma are two such measures.