....Ok and how are you punished? You just stated the part everybody understands.

Literally it says "You can commit sin by making a covenant leader angry" but HOW DO YOU MAKE IT ANGRY

Let's see:
Blade of the Dark Moon - Passing through the wall of mist that hides Gwyndolin;
Chaos Servant - Attacking/Killing the Daughter of Chaos;
Forest Hunter - Attacking any of the Hunters in Darkroot Garden while on the covenant;
Princess Guard - Killing Gwynevere. Also counts as a PVE sin and makes Darkmoon very angry at you.

... but it does tho...
it says what it is
it says how you get it
it says what happens when you get it

What's missing?

And that is why they said it explains sin without explaining what it is you buffoon. The entire concept of sinning in this game is not explained. This page only gives information about sin as a game mechanic.

if you wanna know what sin means go to google you dipshit, this is a game wiki

A Sin is anything that pisses off an NPC or the gods, usually an "immoral" act. The definition is broad because there are many actions that fall under the umbrella of Sin.