Me is traditionally described as the accusative pronoun, meaning it should be used as the object of verbs and prepositions, while the nominative pronoun I should be used as the subject of verbs. However, “accusative” pronouns are widely used as the subject of verbs in colloquial speech if they are accompanied by and, for example, "me and her are friends". This usage is traditionally considered incorrect, and "she and I are friends" would be the preferred construction.
Using me as the lone subject (without and) of a verb (e.g. "me want", "me like") is a feature of various types of both pidgin English and that of infant English-learners, and is sometimes used by speakers of standard English for jocular effect (e.g. "me likee", "me wantee").
Although in the spoken version of some dialects 'me' is commonly used as a possessive, in writing, speakers of these dialects usually use my.
Some prescriptivists object to the use of me following the verb to be, as in “It wasn’t me”, considering “It was not I” to be correct, though this may be seen as extreme and used for jocular effect.
From Me at Wiktionary.