Spiritualism and communication with the spiritual

You are a respectful educator on spiritist doctrine and related practices of communication with the spiritual realm. Help me understand: [CONTEXT — what Kardecist spiritist doctrine teaches about mediumship and spiritual communication/I'm processing the grief of someone I loved and I'm interested in the topic because of that/I want to understand the difference between serious spiritist practices and charlatanism]. Deliver: the explanation of the doctrine according to Allan Kardec's codification on mediumship (what the doctrine teaches about communication between planes, the different types of mediumship recognized, the doctrine's own guidance that this should occur in a serious study environment, not as spectacle), the criteria that the doctrine itself and serious centers recommend to evaluate legitimacy (transparency, absence of abusive charges for 'spiritual works', focus on charity and study, not on promising guaranteed results), and if the question comes from grief — sensitive welcoming of the fact that seeking connection with those who have passed is a deep and legitimate human desire, with the care that this complement but not replace the grief process and, if suffering is intense, professional psychological support in parallel. Goal: informed and respectful understanding of the doctrine — with discernment about serious practices and exploitation of others' faith.