They are only used in some regional dialects today. They are all second person singular pronouns. "Thou" and "thee" are subject and object pronouns respectively and both mean "you". "Thy" is possessive and means "your". There is also the possessive pronoun "thine", which means "yours".

Those are not traditionally used in modern English in less a speaker is trying to act a older variant of English or religious but meaning usually is lost since we don't use them. Early Modern English or older. roughly (1600-1800, some dialect regions now) These all are for the second person (informal) traditional meaning. including thine (or before a vowel same as mine versus my) Thou = you ( for people who are lovers, or for someone who ranks below you. i.e Romeo and Juliet's famous lines, "Romeo, Romeo where art thou Romeo..(I think that is right)" so Juliet is showing her strong affection to Romeo. A King or someone who has 'more power' than you would say thou to anyone who is less than an equal. ) you = you (would be said to someone how is in a higher position, or of equal (fairly sure..). ex: Where are you father (from his children), where the father might say. Where are thou children? etc.. Thee = would be the object of the proposition or the verb. It means "you" in modern English. I saw you, I saw thee what happened to thee (you)? *this is a definition of a accusative or dative case which is lost in Modern Eng. Thy is just your. That is their meaning second person has fallen out of fashion since we "moved" to more equality (not sure if they are used in the same manner). Versus tu versus usted/vous/Lei, in Spanish/french/Italian where it is more familiarity than English where it showed romantic interest or a distinction of their social status. You stayed the same you as we used to today. Hope that helps

In Early Modern English "ye" was formal and "thee" was informal. English no longer distinguishes between formal and informal "you" fortunately. To most modern speakers of English "thee" sounds very formal (contrary to how it was used) and archaic. A modern translation of the story would replace "thee/thou/thy/thine" with "you/your/yours".

I wish we still used these nouns today! but sadly I don't think anyone uses even a remote variation of them; I only see them in old/middle English literature and plays, scriptures and period movies :( here's a quick guide Thou: You, when it's the subject of a sentence like "You are beautiful" Thee: You, when it's the object of a sentence "If they see thee they'll kill thee!" (Shall I compare thee to a summer's day? Thou art more lovely and more temperate) Ye: You, plural form (when speaking to a crowd) Thy: Your (thy life was given for me.) Thine: Yours (my life is thine.) Although, I don't know exactly why or how they morphed into the you, your and yours that we use now. Lets see what others have to say.