1. "я" is just like "I", as the subject.
2. ("меня" is also used after some particular words or prepositions)
3. "мне" is just like "(give) me", e.g. Он звонил мне. He gave me a call.
4. "меня" is just like "me", to use "I" as the object. e.g. Она любит меня. She loves me.
5. "мной" is "by me", "using me" (Instrumental case, I know you'll know that by seeing the name)
6. "обо мне" is "about me" e.g. Мама думает обо мне. Mother thinks about me.