Very high level question! I had to use dictionary! 吾 means I or me. However, it is rather old literary word. I think, 吾　is used in eg) bible or old camous literary works. It is like "Thee" which I saw in English bible in weddings...it means "you", though. hope it helps =)

吾 and 私 are the same certainly meanings. but　吾 is not a kanji of using regularly. 私 and 僕 are usually used.