"Soy" is a verb: am
"Yo" is the subject of a sentence: Yo soy quien responde.
"Me" can never be used as the subject. Me is a substitute of yo, and is always placed near the verb: Mírame = Look at me; ¿Por qué no me miras? = Why don´t you look at me?
"Mi" is a possesive: my.
"Mí"(with ´) is always preceded by a preposition (a, ante, bajo, cabe, con, contra, de, desde, en, entre, hacia, hasta, para, por, según, sin, sobre o tras): Sin mí = without me; para mí = for me.
"Con mí"(with ´) is a mistake; conmigo is correct = with me.