Infractions and warnings are used by staff in response to violations or near violations of the posted rules.
They are an internal system, and there are no explanations on the site as there really don't ned to be any as TFL's stated rules more than adequately put the face to the expectations for how all members are expected to conduct themselves.
Mods issue few infractions without discussing them and arriving at a group consensus.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.